Fine tuning an 850

[Guest]

So, here's the baseline:

• individual foam filters and V&H 4-1
• rebuilt top end with new o/size pistons/rings and lapped valves, valve clearances in spec
• carbs ultrasonically cleaned with all new o-rings, fitted with DJ Stage 3 kit and set as per DJ instructions incl pilot mixture screws at 4.5 turns out, pilot jet Mikuni #45 (this is a size up from USA models), DJ needles on the 3rd notch from the top, no leaks at the carb boots
• Dyna coils and ignition, coil-relay-mod, new sparkplug leads
• exhaust tested for leaks at the headers - no leaks

The problem:

• pops on decelaration quite a lot, through the exhaust
• occassionally pops through the carbs: At a steady speed only, at small throttle opening like 1/8 to 1/4 turn.

Bike idles well and pulls with no coffing / sputtering in any gear at any rpm and from any throttle position (i.e. no noticeable issues while riding other than the two mentioned above).



I had the ignition timed only statically but I would think it's spot on as per Dyna instructions. Though, I'm wondering if the above problems may have to do with the ignition timing rather than carbs settings.


Any pointers?


Thanks for any help

 

[49er]

So, here's the baseline:

• individual foam filters and V&H 4-1
• rebuilt top end with new o/size pistons/rings and lapped valves, valve clearances in spec
• carbs ultrasonically cleaned with all new o-rings, fitted with DJ Stage 3 kit and set as per DJ instructions, pilot mixture screws at 4.5 turns out, pilot jet Mikuni #45 (this is a size up from USA models), DJ needles on the 3rd notch from the top, no leaks at the carb boots
• Dyna coils and ignition, coil-relay-mod, new sparkplug leads
• exhaust tested for leaks at the headers - no leaks

The problem:

• pops on decelaration quite a lot, through the exhaust
• occassionally pops through the carbs: At a steady speed only, at small throttle opening like 1/8 to 1/4 turn.

Bike idles well and pulls with no coffing / sputtering in any gear at any rpm and from any throttle position (i.e. no noticeable issues while riding other than the two mentioned above).



I had the ignition timed only statically but I would think it's spot on as per Dyna instructions. Though, I'm wondering if the above problems may have to do with the ignition timing rather than carbs settings.


Any pointers?


Thanks for any help

Psy, make sure that you don't have any air leaks at the header. I know you had to modify that area, so re check for good sealing. That is one cause of backfiring on decel. The other is running too lean a pilot jet/setting. If you have shimmed the needle, you may now be too lean on the pilot to effect a clean transition to the new needle position.

Don't rely on the static settings for your ignition timing. Recheck it with a timing light and also the rpm that full advance occurs. Your timing won't be causing the pops on decel though.

 

[Guest]

I think you need bigger size pilots... 4.5 turns out is a lot, should be around 2.5-3.0 - try bigger pilots & then re-set the mixture screws again.

Wouldn't hurt to check the timing with a light either - then you'll know if that's right or not...

Good luck!

 

[Guest]

Forgot to say it's CV carbs.

Psy, make sure that you don't have any air leaks at the header. I know you had to modify that area, so re check for good sealing. That is one cause of backfiring on decel.

Ian, I fitted the header, run the bike for a while, then taken the header off and looked for any leaks (on the gaskets/header mating points) but they seal perfectly. Being the perfectionist I added some exhaust sealing paste nonetheless...

The other is running too lean a pilot jet/setting. If you have shimmed the needle, you may now be too lean on the pilot to effect a clean transition to the new needle position.

Pilot screws are at 4.5 turn out as per DJ instructions. They are seating so very clumsily at that many turns out and undoing them even further looks like they'd just pop out.

Pilot jet is #45 which is already a size larger than what DJ kit is made for (as USA bikes have #42.5). When I take the plugs out after idling, they are rather black, so not lean.
Should I try another size up on the pilot (I think I have a set of 47.5s somewhere)?


Would lifting the needle another notch do anything to popping on decel?
Or, is it only the idle circuit that's involved when the throttle is closed and needle position doesn't play a role?

Questions... questions ...

 

[49er]

If your plugs are black on the pilot circuit, you're too rich. However, this contradicts what is happening on decel, when the engine pops.

Did you get the black plugs after a pilot circuit plug chop? If not, you need to do this properly to eliminate the possibility of a rich needle influence on the plugs colour.

Also, those individual foam filters will be adding more restriction to air flow than pods. I believe the suggested settings in the DJ kits are for when using pods.

Are you still running the stock carbs (BS32SS)?

 

[Guest]

Yep, BS32s. Yep, checked the plugs after idling. I can double check... but I also can start the engine from cold with very little choke and on idle I can smell the fuel more than before - all suggesting added richness I would think.

If your plugs are black on the pilot circuit, you're too rich. However, this contradicts what is happening on decel, when the engine pops.

That's why I'm pulling my hair...

 

[49er]

Try 40 pilots, setting idle screws to highest rpm method and test again.

 

[Guest]

Thanks guys.

Any other thoughts from anyone else?

 

[Guest]

So, here's the baseline:

• individual foam filters and V&H 4-1
• rebuilt top end with new o/size pistons/rings and lapped valves, valve clearances in spec
• carbs ultrasonically cleaned with all new o-rings, fitted with DJ Stage 3 kit and set as per DJ instructions incl pilot mixture screws at 4.5 turns out, pilot jet Mikuni #45 (this is a size up from USA models), DJ needles on the 3rd notch from the top, no leaks at the carb boots
• Dyna coils and ignition, coil-relay-mod, new sparkplug leads
• exhaust tested for leaks at the headers - no leaks

The problem:

• pops on decelaration quite a lot, through the exhaust
• occassionally pops through the carbs: At a steady speed only, at small throttle opening like 1/8 to 1/4 turn.

Bike idles well and pulls with no coffing / sputtering in any gear at any rpm and from any throttle position (i.e. no noticeable issues while riding other than the two mentioned above).



I had the ignition timed only statically but I would think it's spot on as per Dyna instructions. Though, I'm wondering if the above problems may have to do with the ignition timing rather than carbs settings.


Any pointers?


Thanks for any help

When I first read your problems, it sure sounded like a lean condition however, when you then posted your plugs are black, I now "recall" my above advice . I still think your mixture screws are turned out too much & perhaps that's what causing at least some (all?) of your issues.

I would try this first:

- turn each mix screw in one full turn & go for a ride
- adjust from there, perhaps 1/4-1/2 turns depending on your plugs.

Of course, you might want to try adjusting them using the highest RPM method first but in any event, I think your richness has something to do with your screws out too far (especially if your pilots are already bumped up).

Good luck,

mike

 

[Suzuki_Don]

If you have shimmed the needle, you may now be too lean on the pilot to effect a clean transition to the new needle position.

PSY - excuse me butting in here but I have a similar problem, not popping back but a flat spot between closed throttle and the needle phase.

IAN - I have shimmed my needles and have a flat spot as mentioned between closed throttle and when the needle comes into operation. As you have said the shimmed needles could mean the pilot is too lean now. What is the best way to fix this situation: with the mixture screw or a larger size pilot jet or a smaller size air jet. Does the pilot jet only feed fuel to the mixture screw or does it also feed fuel to the venturi once the mixture screw has no effect any more? In other words does the pilot jet have a part to play between the mixture screw stage and the cut-away stage?

The issue with mine is not a huge one, not a huge flat spot, just a lag when accelerating out of a corner before the needles "come on". On tighter, slow speed corners I do not feel it because the throttle is snapped right open, it's more noticeable on high speed corners (50mph) where more gradual opening of the throttle is happening.

Thanks.

Sorry for hijacking PSY, but I did not get many responses to my thread on this issue.

http://www.thegsresources.com/_forum/showthread.php?t=178151

.

 

[49er]

PSY - excuse me butting in here but I have a similar problem, not popping back but a flat spot between closed throttle and the needle phase.

IAN - I have shimmed my needles and have a flat spot as mentioned between closed throttle and when the needle comes into operation. As you have said the shimmed needles could mean the pilot is too lean now. What is the best way to fix this situation: with the mixture screw or a larger size pilot jet or a smaller size air jet. Does the pilot jet only feed fuel to the mixture screw or does it also feed fuel to the venturi once the mixture screw has no effect any more? In other words does the pilot jet have a part to play between the mixture screw stage and the cut-away stage?

The issue with mine is not a huge one, not a huge flat spot, just a lag when accelerating out of a corner before the needles "come on". On tighter, slow speed corners I do not feel it because the throttle is snapped right open, it's more noticeable on high speed corners (50mph) where more gradual opening of the throttle is happening.

Thanks.

Sorry for hijacking PSY, but I did not get many responses to my thread on this issue.

http://www.thegsresources.com/_forum/showthread.php?t=178151

.

Don, you PM'd me on this, but I will reply to the group as it may help others.

I read your other post, so here are my views on and a number of points.

Because you are still using your airbox and original carbs, don't change the diaphragm springs or the pilot air jets.

Don't be anal about the Colortune flame results. They are a guide only. I couldn't get my VM's to transition cleanly after setting a blue flame.

Your plug pic indicates a slight richness to me.

You have shimmed the needles. Did you do that to lean it off?

To correctly adjust your pilot mixtures, set all carbs at 3 turns out. Now individually turn each screw in until the engine starts to drop rpm and run roughly. Now open the screw until the engine starts to smooth out. Turn another 1/4 turn out to see if it changes. If it doesn't, you have found the right spot. Repeat for each carb. If you continue opening these screws and the engine doesn't increase rpm, you have started to get too rich. When you end up with this situation, you will experience the same results that you are describing, a flat/fat spot, just off idle position.

All the circuits overlap, so it can take some time to get perfect transitions from 2000 - 10000 rpm You don't need to consider the cutaway on your CV's!

Hope this helps.

 

[Guest]

If you continue opening these screws and the engine doesn't increase rpm, you have started to get too rich. When you end up with this situation, you will experience the same results that you are describing, a flat/fat spot, just off idle position.

I have found out just this when attempting to get rid of the popping - I ended up with a fat spot just off idle (but the popping remained...)

 

[Suzuki_Don]

You have shimmed the needles. Did you do that to lean it off?

Hope this helps.

Ian thanks for the reply. Very helpful indeed.

I shimmed the needles to raise them a tad to richen the mid range. Every part of the range of opening the throttle from idle to full throttle is really, really good except for just off idle, probably about 2000rpm I would say. Although it is also the throttle position more than the revs the motor is at. the mixture screws were set at 2.5 turns out.

I have also just read in the Mikuni Manual that if there is a manifold air leak this will cause a lean condition and part throttle detonation. This is also a symptom that I have. I did not relate it to my carburation problem. I changed from 95 octane to 98 octane and still have detonation on opening the throttle initially. I thought the ignition timing was just a bit advanced. So this is something else for me to investigate. It could be a bit hard to check the tightness of the 6mm carb boot bolts with the carbs in place, but I will give it a go.

 

[Darin Jordan]

Have the carbs been Carbtuned balanced?? My 850G did this same thing, and had a strange "burble" at 1/8th throttle opening or less, and would pop through the exhaust, occassionally popping back through the carbs even.

After I did a good valve adjustment and balanced the carbs with the Carbtune, it's smooth as silk now.

My setup, for reference: 1980 GS850G, Stock Motor, K&N Pods, Mac 4-1 with competition baffle. Dynojet Stage III, 165 Mains, Needles in 3rd slot, 4.5 turns on Pilots.

 

[Guest]

Have the carbs been Carbtuned balanced?? After I did a good valve adjustment and balanced the carbs with the Carbtune, it's smooth as silk now.

My setup, for reference: 1980 GS850G, Stock Motor, K&N Pods, Mac 4-1 with competition baffle. Dynojet Stage III, 165 Mains, Needles in 3rd slot, 4.5 turns on Pilots.

Lucky you Darin!
Yes, the carbs are freshly balanced and valves in spec - and my setup is exactly like yours (except the filters are foam filters...) but it still pops quite a bit.

 

[49er]

Ian thanks for the reply. Very helpful indeed.

I shimmed the needles to raise them a tad to richen the mid range. Every part of the range of opening the throttle from idle to full throttle is really, really good except for just off idle, probably about 2000rpm I would say. Although it is also the throttle position more than the revs the motor is at. the mixture screws were set at 2.5 turns out.

I have also just read in the Mikuni Manual that if there is a manifold air leak this will cause a lean condition and part throttle detonation. This is also a symptom that I have. I did not relate it to my carburation problem. I changed from 95 octane to 98 octane and still have detonation on opening the throttle initially. I thought the ignition timing was just a bit advanced. So this is something else for me to investigate. It could be a bit hard to check the tightness of the 6mm carb boot bolts with the carbs in place, but I will give it a go.

Don, if you have an air leak/leaks your idle should hang up for a short period after closing the throttle. I would also expect your plugs to be showing a lean colour, which they don't.

What compression ratio are you running on this engine? You may be over advanced down low, causing detonation. If it's detonating just off idle, that will give a flat response too. Try retarding the spark a couple of degrees and then retest it. If the pinging stops, but you loose some mid range/top end torque, then you need to use higher octane fuels or fit an adjustable advance curve electronic ignition to correct this.

 

[Suzuki_Don]

Don, if you have an air leak/leaks your idle should hang up for a short period after closing the throttle. I would also expect your plugs to be showing a lean colour, which they don't.

Yes Ian I agree, you make perfect sense. It's good to have a clear head when mine is getting all muddled.

What compression ratio are you running on this engine? You may be over advanced down low, causing detonation. If it's detonating just off idle, that will give a flat response too. Try retarding the spark a couple of degrees and then retest it. If the pinging stops, but you loose some mid range/top end torque, then you need to use higher octane fuels or fit an adjustable advance curve electronic ignition to correct this.

I am running 9.5:1 compression ratio. When I changed to 98 octane the pinging decreased a bit but is still there. If I'm really gentle, gradually opening the throttle I can get away without it pinging, but coming out of a corner on an uphill grade it's really hard to stop it pinging at all. Remember I have a points, condensor setup and the timing is set for the original 550 motor - timing marks, etc. I should probably clean the points up and rotate the whole baseplate a few degrees to retard the timing somewhat.

Below are the details of both ignition timing setups. Mine is currently set up on the GS550 specs. which would mean below 1500 rpm it is advanced 7 degrees more than would be ideal. But with conventional points setup I won't be able to get the timing perfect.

GS650E
Ignition Timing ....................................................... 10? B.T.D.C. below 1 650 r/min and
.................................................................................40? B.T.D.C. above 3 500 r/min
GS550
Ignition Timing ....................................................... 17? B.T.D.C. below 1 500 r/min and
.................................................................................37? B.T.D.C. above 2 500 r/min

 

[49er]

I am running 9.5:1 compression ratio. When I changed to 98 octane the pinging decreased a bit but is still there. If I'm really gentle, gradually opening the throttle I can get away without it pinging, but coming out of a corner on an uphill grade it's really hard to stop it pinging at all. Remember I have a points, condensor setup and the timing is set for the original 550 motor - timing marks, etc. I should probably clean the points up and rotate the whole baseplate a few degrees to retard the timing somewhat.

Below are the details of both ignition timing setups. Mine is currently set up on the GS550 specs. which would mean below 1500 rpm it is advanced 7 degrees more than would be ideal. But with conventional points setup I won't be able to get the timing perfect.

GS650E
Ignition Timing .................................................. ..... 10? B.T.D.C. below 1 650 r/min and
.................................................. ...............................40? B.T.D.C. above 3 500 r/min
GS550
Ignition Timing .................................................. ..... 17? B.T.D.C. below 1 500 r/min and
.................................................. ...............................37? B.T.D.C. above 2 500 r/min
_

Don, your 9.5-1 CR isn't high enough to warrant running anything higher than 91 RON.

Are you saying that you're still running the 550E points system, including the centrifugal advance, but that you have timed it to the 650 specs? If so, that is your problem. Try retarding the spark by at least 5 degs and take the bike for another run. The longer stroke and different chamber/piston dome configurations won't be suitable for that advance rate. You may need to do some mixing and matching of the centrifugal advance mechanisms and the weights/springs too.

 

[Suzuki_Don]

Don, your 9.5-1 CR isn't high enough to warrant running anything higher than 91 RON.

Are you saying that you're still running the 550E points system, including the centrifugal advance, but that you have timed it to the 650 specs? If so, that is your problem. Try retarding the spark by at least 5 degs and take the bike for another run. The longer stroke and different chamber/piston dome configurations won't be suitable for that advance rate. You may need to do some mixing and matching of the centrifugal advance mechanisms and the weights/springs too.

I am still running the original 550 points on backplate setup and it is timed to the original 550 timing marks and has been done statically. It has the original mechanical advance/retard with bob weights, springs, etc. It is not timed to 650 specs as there are no marks on the centrifugal unit for the 650.

Is there a specific way to retard the timing exactly 5 degrees or do I just undo the three screws holding the base plate and move the plate 4mm or so to retard the timing by guess work, etc.

Also I noticed that the points centrifugal advance unit can only advance the timing by 20 degrees and the 650 transistorised system can advance it by 30 degrees.

And Ian thanks for giving me the job of swapping springs and bob weights. This is a joyous job no doubt. Could anyone who has any spare bob weights send them to me please?

I do have the centrifugal advance/retard unit off a GS650, but of course it does not have the cam to open and close the points, but I may be able to use the springs and bob weights from it.

Going by my calculations if I retard the timing by rotating the base plate 5 degrees so things are better at small throttle settings then the timing higher up the rev range will be retarded by the same amount which means it will be advanced by only 32 degrees, whereas the 650 timing is quoted at 40 degrees of advance above 1650rpm. Is this going to cause a problem -- being too retarded at high revs and wide throttle openings.

Thanks again for all help given.

 

[49er]

Hey Don, life gets tedious , don't it?

If you're running a 650 crank in your 550 cases, why can't you use the electronic ignition components made for that setup? You should have minimal tuning challenges this way.

If you do choose to persevere with the points and weights, use a fine tipped felt pen to mark the edge of your backing plate at a point adjacent on the ali housing. I use the crankcase joint seam as my reference. Now just back off the static timing as much as it takes to prevent pinging. You may run out of adjustment on the backing plate and need to extend the slots to achieve the desired timing position. Once you've found this point, use the pen to mark the housing. You now have a distance that you can calculate and convert into degrees of crank rotation, or you can use a degree wheel to confirm the exact figure. The figure isn't important, but finding the correct static advance is.

At present, you are starting too advanced and continuing that way as the revs increase. The 550 weights will be lighter than would be required for the slower acceleration of the 650 crank. So you need to add some weight or fit stronger springs.

I would save yourself some agro and fit up a 650 electronic unit if its available.
One benefit is that you get a more accurate advance curve, up to 3500 rpm instead of the 2500 rpm with the 550 centrifugal advance system. As an example, the Boyer Bransden system I run on my 850 isn't fully advanced until around 4500 rpm.

Hey, it's decision time mate.