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1327 rich at 5000 carb problem?

  • Thread starter Thread starter kz
  • Start date Start date
K

kz

Guest
Anybody who has any idea why the engine is to rich in fuel att 5000 rpm at full throttle?

The engine is a 1150 rebuilt to 1327, modified cams, head work, bigger valves and Mikuni RS 36.

I suspect the carbs, but which jet to change?

According to my knowledge it's only the main jet that influates the full throttle position?

Could it be related to the cams?

Power and Air/fuel graph link:

http://www.karl.zellner.com/Dynojet1327-1.jpg

Any suggestions welcome....
 
How do you know its rich?

Have you tryed pulling the choke on at 5000rpms to see if it worsens.

Is the throttle wide open?

Needles maybe, one notch lower. Smaller mains. Carter
 
The mains are probably too big. If you can, test the bike at 1/2 throttle for a couple of miles and do a chop test for the plugs. If the plugs are a good color, then you know the needles are good and you need smaller mains.
 
Carter Turk said:
How do you know its rich?
Click to expand...

Measured with lambdasond, its the lower curve in the link.

If I pull the choke it gets worse.

Yes, the throttle is "wide open", the curve in the link is mesured in gear 4 at full throttle.
 
KEITH KRAUSE said:
The mains are probably too big. If you can, test the bike at 1/2 throttle for a couple of miles and do a chop test for the plugs. If the plugs are a good color, then you know the needles are good and you need smaller mains.
Click to expand...

I have tested several mains, if I install even smaller mains it's to lean in the high area after 7000 rpm.

The air jets for the high rev. area are now plugged, so it is not possible to install even smaller mains.

The bike operates fine at half throttle.
 
kz said:
KEITH KRAUSE said:
The mains are probably too big. If you can, test the bike at 1/2 throttle for a couple of miles and do a chop test for the plugs. If the plugs are a good color, then you know the needles are good and you need smaller mains.
Click to expand...

I have tested several mains, if I install even smaller mains it's to lean in the high area after 7000 rpm.

The air jets for the high rev. area are now plugged, so it is not possible to install even smaller mains.

The bike operates fine at half throttle.
Click to expand...
Then all I can think of is maybe different needle jets?
 
With that big of an engine i would'nt think the 36's would run rich in that one area. I'm thinking it could be some reversion going on in the exhaust system. What type of exhaust and cams are you running. Also what is the cam timing set at and what size mains are you using.

If I had a 1327 i'd slap on a set of 40 trons.
 
RacingJake said:
With that big of an engine i would'nt think the 36's would run rich in that one area. I'm thinking it could be some reversion going on in the exhaust system. What type of exhaust and cams are you running. Also what is the cam timing set at and what size mains are you using.

If I had a 1327 i'd slap on a set of 40 trons.
Click to expand...

I have V&H Megaphone, http://www.vanceandhines.com/spm4.html first a had the damping part? (don't know the name in english) with smaller hole.

As I changed to the the damping part with bigger hole the engine ran better and was not that rich any more.

I don't know the exact part nr of the cams, but they are called "modified".

Sorry my english...but what does "If I had a 1327 i'd slap on a set of 40 trons." mean? Is 40 trons an exhaust sytem?

EDIT:

You must mean RS 40 carbs, I thought of that but decieded for RS 36 because I thought the low range would not work on the street with RS 40.

I'm getting the feeling that either the cams, exhaust or camtiming is the reason for the engines behaivor......

Maybe the headporting?
 
KARL - PLEASE READ......

KARL - PLEASE READ......

Earl & Krause can check me on this.

All the posts are accurate. Could be all those things. That's the joy of carburation. 4 major principles.......

1) START FROM THE END RESULT- is it rich or lean? When?
2) USE PROPER TESTS TO DETERMINE MIXTURE SETTING.
3) Check the simple basics first. (Mains first, then needles, pilots rarely)
4) Know your goal or target for the engine (peak HP? vs good midrange & torque?)

Krause said it - your needles are too rich. Here is the fun. Not only does the main impact the needle setting by about a half to one notch with a size change, the TAPER of the needle is important, and no main jet or needle height change in the world will fix that. I know, I tried for 4 years.

First, to wide open throttle - get main jet dialed in first. Put it on a dyno and use an exhaust sniffer. Set your CO to 3 to 4% (street). Plug should look light tan and be tan down in the deeper recess of the insulator.

Next, set your needle. Leave the mains alone. There done. Check needle by running at about 1/4 throttle and 5000 rpm - 60 mph. Ride steady for some miles. Take a plug reading. If tan at the tip....your in.

Check acceleration mode. Whack the throttle in a roll on - should be responsive. Engine should grunt and pull hard. If not, your needle TAPER is off. It is hard to tell a lean condition here....but you can. If the bike pulls harder when throttle is whacked when cold....the taper is too fast (too rich). If pulls harder when hot, the taper is too slow (too lean).

Conclusion, if your around town mileage is good and plug reading of the needles at steady cruise is tan at the tip, AND you find the above needle test indicates the too rich problem you talk about, do one of 2 things:

Slightly open up your air box, this will compensate for the too fast needle taper in acceleration mode (throttle whack) but is the (poorer choice) because it can affect the mains, OR

Go to a slower (more gradual) taper on your needles. They are richening up too fast.

Airbox changes when opening them up require the taper of the needles to be faster. Stock needles tend to need changing when airbox is played with.

CAMS and timing are all relative. Any engine can be adjusted with carburation changes mostly. If you are pleased with your peak horsepower and some of the combinations you've tried have given you good midrange, leave the cams alone. All of this stuff interacts of course, so, where you start is your choice. You must know what your target is.
 
kz said:
Sorry my english...but what does "If I had a 1327 i'd slap on a set of 40 trons." mean? Is 40 trons an exhaust sytem?

EDIT:

You must mean RS 40 carbs, I thought of that but decieded for RS 36 because I thought the low range would not work on the street with RS 40.

I'm getting the feeling that either the cams, exhaust or camtiming is the reason for the engines behaivor......

Maybe the headporting?
Click to expand...

40 trons would be 40mm lectron carbs, pretty much a drag racing only carb. The RS36 carbs should work fine for you, though they do seem a bit small for your engine. You'll be losing some top end, but you should be able to tune them so they run well. Just in case you care to know, I'm running the RS38's, on my 1229, and have no issues with the low end. That's with the same exhaust as you have, G4 cams and some mild porting.
 
Just a thought. What is your cam timing set at? If they are set at 112+degrees, carburetion can be very difficult to set.
 
Re: KARL - PLEASE READ......

Re: KARL - PLEASE READ......

That is an excellent post Tony! Cheers

Earl :-)


Tony Dieter said:
1) START FROM THE END RESULT- is it rich or lean? When?
2) USE PROPER TESTS TO DETERMINE MIXTURE SETTING.
3) Check the simple basics first. (Mains first, then needles, pilots rarely)
4) Know your goal or target for the engine ......................................quote
Click to expand...
 
Thanks for all your replys. :D

I think i will stick to the RS 36 carbs.

I will check the needle taper and the cam tiiming.

I'm of course aiming at max hp AND best mid/low range, but I'm aware of that I have to choose, and in my case I choose the low/midrange even if I loose a couple of hp at high end, thats the reason I choosed RS36 and not RS 40 in the first palce.

I know that the engine is running rich at 5000 rpm and full throttle, because I tested it in the dyno with an Air/fuel ratio sensor (lambda)

If I run with 3/4 throttle or less the problem does not occur.
 
Since you want more mid-range and the widest powerband, I would set the cam timing to 106 degrees, both intake and exhaust. Everyone seems to agree this is the best compromise between top end and low/mid-range power.
Who knows, this may also eliminate your problem, or at least eliminate one more possible cause.
 
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