Trevor's 81 1100 carb jetting issue

[Guest]

Hey all. I'm trying to dial Trevor's 81 1100 in and am having an issue. The engine is stock, V&H 4 into 1, stock airbox with a K&N filter with the lid off. A dynojet kit was put in by his mechanic (not me). The issue is at 8000 rpm the bike starts to sputter, like it's searching for more fuel. We keep increasing the main jet, currently we're at Mikuni 127.5's and I can't believe we need to go bigger than that. We were using the DJ mains but read in a few places that using Mikuni's can sometimes resolve issue's. Swapping to the Mikuni's did help but not completely. Pilot jet is stock and the main clip is in the middle. Can't remember where the mixture screws are currently but I think somewhere around 3-4 turns out. The bikes pretty spot on everywhere else but the 8000 above mark. Intake boots are good, just put in brand new airbox boots and the carbs have been cleaned. Help me if I'm wrong, if the main jet is too big when you go WOT the bike will slow down or bog a bit and you can smell fuel, right? if it's hesitating/searching at WOT then you need to go bigger on the main jet, right?

 

[niclpnut]

Is the filter oiled correctly?

 

[Guest]

Yes, and the bike definitely runs it's best with the lid off. Everything kind of says to me to increase the main jet but it just doesn't seem right that we need to go as big as a Mikuni 130

 

[Steve]

Hey all. I'm trying to dial Trevor's 81 1100 in and am having an issue. ... Help me if I'm wrong, if the main jet is too big when you go WOT the bike will slow down or bog a bit and you can smell fuel, right? if it's hesitating/searching at WOT then you need to go bigger on the main jet, right?

Stop guessing and do a "plug chop". :-k

Find someplace where you can to a run to get it to 8000 RPM, hold it there for a few seconds. Pull the clutch and hit the "kill" switch, coast to a stop in a safe place. Look at the plugs. They will tell you what is happening inside the cylinders.

.

 

[Guest]

Stock ignitions do not like added fuel from stock and the petcocks tend not to flow as fast as you like.
On my first build I was having the same problem and a Dyna-S and Pingel valve fixed me up.

 

[huntb]

Dynojet kit? Did the "mechanic" remove the vent tubes from the carbs?

 

[Guest]

Trevor's mechanic is pretty good, he's the only mechanic I recommend to anyone with a bike but we'll check that when we go back in there, although I'm not 100% sure what you mean by "vent tubes", the only ones I know of are the 2 up top with hoses to them. Chef, I thought about the petcock thinking it wasn't working properly but it is, and I get what you're saying about the Pingle flowing better but Trevor's 83 1100 had the exact same set up with exhaust and carbs and ran perfectly, that's the weird thing about this at first I thought 'easy' just copy what is in the 83 and the 81 should run perfectly since it's the exact same set up....wrong.

 

[Guest]

Yeah do the plug chop and see what they are saying. As for what I would do and this is my opinion, I would start back at square one. I would pull the carbs and go through them just to make sure they are fine. I would pull the DJs out as well and find out what the stock jets were and go from there. I would step up the main jets 2-3 sizes to begin with then bench sync them. Reinstall the carbs, put the air filter cover back on, set the idle mixture screws and sync the carbs. You said the petcock was flowing okay, maybe so, though in the past I've had trouble with the petcock flowing at times when the rpms were above 6,000+ vacuum is barely strong enough to hold it open, hence starving for fuel or would just flat out shut off. As for the coils, I installed the ACCEL super coils on my bike 32 years ago and they haven't missed a beat. That's what I would be looking at.

 

[storm 64]

I would say 1 and 4 carburetor bowls are drying up. I had the same problem on my race motorcycle using stock 1982 1100 carburetors. What I did to fix the problem was I drilled a 3/16 hole on the outside of 1 and 4 carburetors and tapped a 1/8 pipe tap. Then threaded a barbed hose fitting. So I had the main fuel line in the middle with two axillary lines going to 1 and 4. It worked great but looked kind of funky. You may be able to just put fuel tee's between 1-2, 3-4

 

[huntb]

Trevor's mechanic is pretty good, he's the only mechanic I recommend to anyone with a bike but we'll check that when we go back in there, although I'm not 100% sure what you mean by "vent tubes", the only ones I know of are the 2 up top with hoses to them.

Maybe the 1100 carbs don't have them, but when I installed the DJ kit on my 650 I had the same issue until I RTFM. The two vent tubes betwen carbs 1&3 and 2&4 needed to be removed

 

[Katarat]

I have an 80 GS1100E with the same airbox set up w/no lid, 117.5 Mikuni mains and a Pengel petcock and it pulls clean all the way out. I am at 3600 ft though. I agree that its running out of gas but Im no expert

 

[Guest]

Great suggestions everyone. We won't have time to get back at her till next week but I'll be posting up once we do for sure.

 

[BigD_83]

Maybe the 1100 carbs don't have them, but when I installed the DJ kit on my 650 I had the same issue until I RTFM. The two vent tubes betwen carbs 1&3 and 2&4 needed to be removed

I'm trying to picture the rationale for removing the tubes. I know plenty of people have reported success with doing so, but I've never quite understood the physics behind it

 

[TxGSrider]

Guys, this may not apply here, but on cars and atvs if the gas tank isn't vented correctly it will cause very similar conditions. Also, maybe check the petcock screen and any of the little screens up underneath the float needles inside the carbs.

 

[Katarat]

If a carb vent is plugged it will not run on that cylinder. Learned that one the hard way.

 

[Guest]

mikuni and dyno jet use different sizing eg a 130 mikuni main jet is larger than a 130 dyno main jet

 

[Nessism]

In the old Motorcyclist magazine 1100E header test article written by Joe Minton, he used 122.5 mains with the airbox lid off for all his testing. I suspect this is a conservative number but not sure. Sounds like you guys are on the rich side.

 

[trevor]

In the old Motorcyclist magazine 1100E header test article written by Joe Minton, he used 122.5 mains with the airbox lid off for all his testing. I suspect this is a conservative number but not sure. Sounds like you guys are on the rich side.

Yes ,but why does it act like it's starving for fuel at 7-8000rpm?

 

[trevor]

mikuni and dyno jet use different sizing eg a 130 mikuni main jet is larger than a 130 dyno main jet

Yes, we know that. Thanks though. I have a chart with the differences.

 

[Nessism]

One thing to try is to take off the ignition cover and twist the rotor with your hand. You should be able to rotate the rotor about 10 degrees or so and it should spring back easily when you let go. If for some reason the mechanical advance unit is binding you can get a hesitation or even a cap on the engines ability to rev.