A question for the tuners

[Wheelie]

This will be a bit lengthy.

The set up:
'78 GS1000. V&H 4into1, K&N pods, Dyna jet stage 3 kit (142 mains, e-clip 3rd from top, fat spacer on top), ported head, Mega Cycle cam (can't remember the #'s , but next up from stock) Dyna ignition and coils. Compression is a bit weak at around 112psi but consistent.
Electrical system is upgraded with relays for better power to the ignition circuit.
Carb boots and o-rings are recent and show no signs of leaks.
Carbs are in synch but with a weak vaccum level.

The problem:
Set the choke and push the starter and it turns on (like a light switch). Idle on choke is a bit iffy. Adjust the choke a little back and forth in the first minute and it settles in to a decent 2500 high idle. After another minute on choke the RPM's will start to climb and level out a 5000. We try not to do that to often. Choke off and it idles nicely around 1000 rpm.

Start to drive (1/4 throttle) and it leans out pretty quickly, you can pull up on the choke a bit and it runs better. If you don't play with the choke, it coughs and spits and generally bitches a whole lot. With the choke on the side of the carb, you can imagine what fun it is to drive.

If you decide to pull the baffel out of the exhaust and and have some fun, the thing is an animal. I don't have any numbers, but can keep up with my friends Yammi R1 to aruond 110 mph.

The question:
Because of the head porting and cam, even with the bigger jets from the stage 3 kit, is this thing still to lean? Even with the low compression?
Yes the pipes are blue.
What about taking the head to my brother-in-laws machine shop and milling the carb ports so I can install some 36mm flatslides?

Thanks for any help you can give,
Steve

 

[GS850_Coug]

Weak compression due to worn rings also leads to weak vacuum (because intake on the stroke it is sucking air into the cylinder past the rings, instead of through the intake system), which leads to lean condition under throttle. I really think if you solve the low compression you will probably solve the weak vacuum/lean condition.

 

[49er]

This will be a bit lengthy.

The set up:
'78 GS1000. V&H 4into1, K&N pods, Dyna jet stage 3 kit (142 mains, e-clip 3rd from top, fat spacer on top), ported head, Mega Cycle cam (can't remember the #'s , but next up from stock) Dyna ignition and coils. Compression is a bit weak at around 112psi but consistent.
Electrical system is upgraded with relays for better power to the ignition circuit.
Carb boots and o-rings are recent and show no signs of leaks.
Carbs are in synch but with a weak vaccum level.

The problem:
Set the choke and push the starter and it turns on (like a light switch). Idle on choke is a bit iffy. Adjust the choke a little back and forth in the first minute and it settles in to a decent 2500 high idle. After another minute on choke the RPM's will start to climb and level out a 5000. We try not to do that to often. Choke off and it idles nicely around 1000 rpm.

Start to drive (1/4 throttle) and it leans out pretty quickly, you can pull up on the choke a bit and it runs better. If you don't play with the choke, it coughs and spits and generally bitches a whole lot. With the choke on the side of the carb, you can imagine what fun it is to drive.

If you decide to pull the baffel out of the exhaust and and have some fun, the thing is an animal. I don't have any numbers, but can keep up with my friends Yammi R1 to aruond 110 mph.

The question:
Because of the head porting and cam, even with the bigger jets from the stage 3 kit, is this thing still to lean? Even with the low compression?
Yes the pipes are blue.
What about taking the head to my brother-in-laws machine shop and milling the carb ports so I can install some 36mm flatslides?

Thanks for any help you can give,
Steve

You are too lean on your pilot circuits. You don't mention the pilot jet sizes. The fact that once the engine is warm, it still responds better when choked and the pipes are blued, confirms your lean condition in the lower rev range.
Check the fuel mixture screw adjustments (should be 3/4 to 1 turn off the seat). If they are set in this range, you need to go up one size in your pilot jets.
You say that the vacuum level was low when you synched the carbs. What figure are you talking about?
Your compression figure of 112psi is on the low side, but not low enough to cause horrendus blowby at the rings from 1500rpm and upwards.

Milling the inlet ports to accept 36mm flatslides may be premature. Get it running right on the present carbs and re-access. You may decide to give the top end a refresh in the near future. That's the time to do the milling.

 

[Wheelie]

The top end is pretty tight, that was all done when the head was ported, less than 2000 miles ago. The pilot jets and the needles are the ones from the stage three kit. Mixture screws are around 1 3/4 turns and the pilot screws are at 1 1/2 turns. As far as low vaccum signal, the mercury stays in the lower quarter of the tubes. I can't give you a number because I lent that tool out ( note to self, don't lend out your tools).

I forgot to add the fact that the plugs (Denso W24ES-U)are fairly dark. Not black and sooty but a bit rich. If you free rev it, you get black smoke from the exhaust.

Kind of dopey not to include that info in the first place.

 

[49er]

The top end is pretty tight, that was all done when the head was ported, less than 2000 miles ago. The pilot jets and the needles are the ones from the stage three kit. Mixture screws are around 1 3/4 turns and the pilot screws are at 1 1/2 turns. As far as low vaccum signal, the mercury stays in the lower quarter of the tubes. I can't give you a number because I lent that tool out ( note to self, don't lend out your tools).

I forgot to add the fact that the plugs (Denso W24ES-U)are fairly dark. Not black and sooty but a bit rich. If you free rev it, you get black smoke from the exhaust.

Kind of dopey not to include that info in the first place.

Good feedback.
Your compression figures are low for an engine with nearly 2000miles since a rebuild. Did you hone and re-ring, or fit new O/S pistons, rings etc? Have you checked your valve clearances? Did you do the compression check with the engine warm and the throttle wide open?

After re-reading your original post, it appears that you were having problems past the 1/4 throttle position, not up to it. If that is the case, then your needle positons need to be richened. I make this call on the fact that adding some choke at this part of the rev range improved the engine's performance.
Also, your plugs indicate a rich condition on the pilot circuit. Your mixture screws should be set in the 3/4 -1 turns off the seat. Yours are set at 1 3/4 causing it to run rich in the lower rev range. Adjusting these screws to the recommended range should stop the black smoke when "free reving it" and improve the throttle response down low.
Once adjusted, take the bike for a road test and do some plug chops at 1/4, 3/4 and full throttle. These plug reads will tell you exactly what needs changing/adjusting, ie pilots, needle position, or main jet.

It's a shame you didn't do that milling job on the ports when you last had the engine apart. I guess the 36mm flatslides weren't in the equation at that time.

 

[Wheelie]

Valve clearences are good and compression was checked correctly. Didn't do a total rebuild, just the top end. Saving up $ for the new pistons, rings and bore.

I have a real nice original exhaust and scored an original air box from TomMLC. I was thinking about de-tuning the thing to get the drivadility back. It's a lot of fun to kick sport bike butt, but to be able to cruise around town and daily transport is more appealing to me.

I'm pretty sure my lean condition is below 1/4 throttle but it's tough to remember. I'll try to get it out Sunday to test it more. See if I can pinpoint the problem areas better. I've moved the needles so many times I'm tempted to put them in with Velcro.

 

[Wheelie]

Well I didn't get to do the plug chops this weekend due to work and rain. What I did do was go back and check a few things.

Valves are all set at .004" which is where the Mega Cycle spec sheet says to put them. Their online catalog says intake should be at .005" and exhaust at .007". I'm going to change the clearance to the looser settings. My buddy Shaw always says a loose valve is a happy valve.

Now here might be a problem. Since I have adjustable timing gears, I threw the degree wheel on. Intake is right on. Exhaust is 10 degrees retarded. Sounds like I might be on to something here. What do you guys think.

Steve

 

[terbang]

My buddy Shaw always says a loose valve is a happy valve.

Steve

Hmm. Yes happier than a tight one but still not as happy as a correctly set one..
Cheers B

 

[SqDancerLynn1]

Low compression readings are probably due to the cams having more overlap- bleading some of the compression off. Need to bump the compression up

 

[Wheelie]

My heads starting to spin!
O.K. here we go.
My cams are Mega Cycle 38100 and 38105 (intake and exhaust). The cam timing card says to use .004" valve clearence on both intake and exhaust. This is a bit looser than stock (.001"-.003") so I take a look at their website just to be sure and it says to run .005" intake and .007" exhaust. Well now I think some one made a typo, so I call them up. The tech department says to run .006" intake, .008" exhaust. They haven't changed their product, just their recomendations.
It seems I'm getting into noisey valve train territory. These are mild cams .354" lift and 254 duration.
Can someone get Lecroy or RacingJake or other non stock cam guys to chime in?
What valve clearances are others using?

I put the exhaust cam timing back in spec today. One thing off the list.

 

[KEITH KRAUSE]

If those mods are done correctly, the bike should be under carbureted. The 26's can't flow enough for the porting and cams to benefit. Better carbs would be a good choice/match. Anyway...
Your compression is borderline in my opinion. Combustion will be compromised. I see know way your current jetting would be showing dark plugs, that's why I think the compression is effecting it. Are you positive you have the timing on the Dyna ignition correct and it's advance is operating correctly? The lower vacuum reads would make sense with low/poor compression. I wonder if the porting was done poorly?
The 142 mains are the correct choice in the DJ kit. The 138's work fine for a quality pipe/K&N's/1085 kit. 142's for anything beyond that, done correctly.
No way that the e-clips in the 3rd position from the top of the DJ needle and the factory plastic spacers installed in correct order would create a rich 1/3 throttle position plug read. The plugs should be reading quite lean actually. You need a MINIMUM 4th position and maybe the clips in position 5 with the jetting spacer directly on top the e-clip (position 4 1/2.) The stock pilot jet should work fine. I'd probably try the pilot fuel screws at 1 1/2 turns out initially. The side air screws at 1 3/4 and then fine tune with the highest rpm method if it will allow you. Test at minimal throttle position for the pilot circuit.
Be sure the two floatbowl vent lines are removed and the ports left open, a requirement in the DJ stage 3 kit info.
Don't over-oil those K&N's. Easy to do. If any doubt, clean correctly and re-oil.
To back up a bit, I'd also re-bench synch the carbs. Then after re-start, fine tune the side air screws and then vacuum synch. Set any higher level(s) you initially see DOWN to meet the lower ones. If no mechanical/compression/flow issues, the levels you see are fine. But that brings us back to the possible compression/porting, etc, issues.
Those dark plugs and (from my experience) lean jet needle positions just don't add up if the bike was in otherwise decent tuning condition.

 

[Wheelie]

And the GS pod guru chimes in.
Nice to hear from you Kieth and thank you for joining in.

Now that I've got the cams in the right spot, my next step will be to figure out and set the correct valve lash. Once that is complete I will do as you suggest and start at step one again with the carbs. I'll fire it up and re check the compression as I'm going off memory on that one. This will also show any effects from re-positioning of the cams. I'm sure a 1085 kit is in my future.

Porting was done by a reputable machinist and the work looks good, but I couldn't say if it is correct for my setup. Never did ask how many 2 valve Suzukis he had worked on. My mistake. In retrospect I would not do this again for a street bike. I never did intend to race this, just got carried away.

Any ideas on the valve clearence thing?

 

[KEITH KRAUSE]

I really don't know enough about aftermarket cams to advise about the best clearances/cam timing. Stock cams are best set at 106 degrees for best powerband and if you like more top end, about 108/110 in my opinion.
Reading back on a couple things...your compression isn't at the service limit(100PSI), but it's below the lowest "standard" range of 128. Per factory manual info.
What are these relays you mention that improve the Dyna ignition system?? I can't see where they're needed on a clean/correctly operating system. Your spark at all four is a healthy bluish/white?
Still scratching my head over the dark plugs with what I believe to be lean jet needle adjustments and sensible main jet choice, though you didn't say what throttle position tests gave you the dark plugs.

 

[Wheelie]

The standard Bosch 5 terminal auto relay. Installed it to ensure a good power source to the ignition system. Spark is not the problem, a big fat blue white spark it is.

I think I'll get some new plugs and get a little more scientific about my testing. Do the plug chops like 49er suggested. Try to get more specific about the runnig condition so as to make it easier for you guys to assist in my mess.

Thanks to all
Steve

 

[KEITH KRAUSE]

OK. I guess 49er and I differ a bit about the necessary throttle positions to make the 3 basic jetting circuit tests at.
My opinion is to test the main jets at full throttle. Test the jet needle at 1/3. Test the pilot circuit at minimal throttle openings. Mark your throttle grip and housing if any doubt.
The idea is to try to eliminate any overlap effect between circuits. On your VM carbs, the jet needle comes into effect much sooner than many realize, especially with the different DJ needles. A minimal throttle opening will show you what the pilot circuit is doing with the very least possible overlap effect from the jet needle. All you need is the mimimum. Testing the jet needle at 1/3 also eliminates any effect from the main, which will kick in at 3/4 throttle.
There's lots of charts on this stuff that show when this and that kicks in. They can be different enough to confuse. For these VM carbs, I have my own chart in my head.

 

[Dave8338]

When in doubt, go with Keith on the numbers. He brings LOADS of knowledge to the table, when it comes to these bikes, modded...no disrespect to all others who know ten times as much as I, about the GS.

I'm sure you've seen this somewhere else, but if not, it seems to be the most straight forward, method oriented, carb tune procedure that I've read, as it pertains to bikes. I'm a carb freak (mostly 650CFM and above)and have read numerous books/articles on various carb tune procedures, and as far as I can tell, when starting from scratch (heavy mods, one size does not fit all), this method will get you from start to finish and not leave you guessing. My .02 cents. http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Dave

 

[49er]

OK. I guess 49er and I differ a bit about the necessary throttle positions to make the 3 basic jetting circuit tests at.
My opinion is to test the main jets at full throttle. Test the jet needle at 1/3. Test the pilot circuit at minimal throttle openings. Mark your throttle grip and housing if any doubt.
The idea is to try to eliminate any overlap effect between circuits. On your VM carbs, the jet needle comes into effect much sooner than many realize, especially with the different DJ needles. A minimal throttle opening will show you what the pilot circuit is doing with the very least possible overlap effect from the jet needle. All you need is the mimimum. Testing the jet needle at 1/3 also eliminates any effect from the main, which will kick in at 3/4 throttle.
There's lots of charts on this stuff that show when this and that kicks in. They can be different enough to confuse. For these VM carbs, I have my own chart in my head.

Yes, we do vary a bit on the throttle testing positions. We agree on the main jet testing proceedure. I agree that the Main jet is the starting point as suggested in the link provided by Dave 8338.

There have been numerous posts on this subject, and they wary greatly depending on the engines state of tune, and the resources available to the tuner. I intent making this my last post on this subject.

When we say 1/8 or 1/4 throttle, the actual amount of throttle travel at the grip will vary from model to model and bike to bike. Many GS owners report that they have up to 1/2 of a full grip rotation, when at full throttle. On my bike, I have 1/4 grip rotation at full throttle. It becomes quite difficult to tell when you reach 1/8 of full throttle, or 1/4 for that matter, just by feel. IMO, it's not a safe practice to mark the positions on the grip so you can visualise while riding/testing.

The reason that my throttle testing positions are a little higher than Keith's is because a believe that the pilot circuit does still have a significient influence on the smooth transition between the pilot and needle circuits.
If you have unlimited resources, you will have a bucket of jet needles with varying diameters and tapers that will lead you to getting the optimium performance right through your rev range.
In reality, most of us have stock needles or something very close to them. When we experiment with oversized rebores (raised CR's) aftermarket 4-1 exhausts, porting, cams, pods etc, the engines scavenging characteristics can drasticly change the demands on the mid range (needle circuit). To compensate for this, I have found that plug chop testing the pilot circuit up to 1/4 throttle confirms whether the transition air/fuel ratio is correct. Throttle response from idle and up to 2000 rpm, will tell if the pilot jet is too lean or too fat. Progressing from that, your plug readings at 1/4 throttle will influence you whether to raise or lower your needle position.
The test at 3/4 throttle is to confirm that the needle position is correct.
This is the point where the main jet takes over. In reality, the test is done slightly before 3/4 position.
All the plug chop tests should be done when the engine is under load, not cruising on level ground.
And carburettors with pump jets, well that changes the ball game again.

 

[KEITH KRAUSE]

Well, I must admit I wasn't even going to say a thing about what throttle positions should be used.
I've been a member here a long time and I know how easy it is for someone to think their toe's been stepped on. That was not my intention. 49er certainly makes an effort here to help and it's appreciated. He's helped me understand specific things better. Since it's his last reply here I can tell he thinks I stepped on him. He knows how serious I take carb advice and I'm sorry if it looked like I tried to improve on his method or whatever you'd call it. We both have our way and I guess the reader can do/decide what he likes.
My advice in this case, relates to the exact carb and generally the exact model the person asking for help has. He has VM carbs and a 78/79 1000.
The pilot circuit is best tested at minimal throttle. Beyond that, the slides cut-away briefly takes over before the jet needle takes over. On the VM's, 1/4 throttle is well into cut-away range and there's no sense testing the pilot circuit when you're in the cut-aways range. The DJ jet needles do allow the jet needle to have effect sooner than the stock needles. At 1/3, or some would even suggest 1/2 throttle, you're positively on the jet needle. At approx' 3/4, there's too much overlap between the needle and main to positively test for the main there, so full throttle is no doubt for the main. I've always advised marking your throttle if you have any doubt at where the throttle is. I suppose it could add a bit to the danger of high speed testing but I thought testers capable of it. I can't get into how various models use different throttles and how it effects the amount you are truly opening the carbs. Too technical. I just open the throttle to the needed amount. I've never personally needed to mark a throttle, but some may benefit from it. Their choice.
Also, testing under load is correct when reading plugs, but when testing the pilot circuit, minimal throttle should be used and is adequate. Such small throttle openings and being under a load don't really go hand in hand. I mean, you must open the throttle beyond the correct range to really apply a significant load. Moderate acceleration isn't what's needed here. A steady speed around town, just general/easy riding around, will give you a fair idea of what the pilot circuit is doing. On the other two circuits in question, 1/3 and full throttle are certainly load related enough.
My opinions on best throttle positions are based on a true separation of the circuits. Minimal, 1/3 and full meet that need.
Anyway, sorry to get on anyones nerves. Smiley...see?

 

[Einar J Skog]

Hi

About cam clearence..


I have set the valve clearence to 0.1 mm (0.004 inch)