1978 1100 Rich at low speeds. Help

[Diskman01]

1978 E. 33K miles. Searched and read everything I could on here.. Need some ideas.

Synced carbs, replaced plugs with NGK bp6es, adjusted the floats to 26MM. A plug chop on a 100 mile trip at 75MPH shows a nice light tan to maybe a tad lean but not bad at speed. Around town it will chug, burp and pop out the exhaust. Plugs will turn a dark black after about 5 minutes of in-town driving.

If I lean out the idle mix screws 1/2 turn more I will get a hanging idle at 2500-3000RPM at stoplights. sucks. Plus it just acts lean at idle then..

Ideas? It's acting lean on low end and really rich just off idle. A bit of choke at hot idle and the engine speeds up. Seems that the "mid" range is too rich. The throttle has a very "flat" spot just off of idle up to 3K. If I hold it it 35MPH it will start burbling and smelling too rich. Apply more throttle and it clears up and goes like a scalded cat above 3500RPM.

Mains are 137.5s, pilots are STOCK 45s (verified visually STOCK). Main needle clips in MIDDLE position. UNI Pods with Home Depot stacks and some noname 4 into 1 exhaust..

Previous owner replaced the coils and wires. I checked the pickup wires while running and with a meter stopped. They are fine. Spraying carb cleaner around the carbs while running doesn't speed up at all.

Im at wits end. Anyone have ANY more ideas before I give up and list her on craigslist? (just kidding) Highway driving is smooth but around town it really sucks and is just not cool with it burping and farting and acting rich.


Thanks for reading.. Here are my 2 troublemakers.

[ManagerMike]

Have you tried running with the "choke" at the first detent?
It isn't a choke per say, as it doesn't resrtrict air inflow. Rather it opens an enrichmient circuit. I'm not there to hear it run, so I'm just tossing an idea out there, but it is possible you are running too lean instead of rich (you stated the idle steps up with choke when hot).
An improper mixture, lean or rich, results in incomplete burn of the air/fuel mix and can blacken the plugs and cause backfire, particularly at lower rpms.
I have pods and stacks and a custom 4-2 exhaust on my 78 and switched from the stock 137.5 mains to 145's (I kept the 45 pilots) and gained all kinds of power at low to midrange as well as boosting the higher rpm bands.
Just an idea, as requested. Good luck!

[petejw]

i was thinking the same as mike,
could it be lean, float heights should be set at
25.7, 26mm puts the float heights at a leaner setting from stock,
i know .3mm doesnt sound like much but its enuff to make a difference,
also a lean float level would make the bike run/accelerate 'flat'.
float heights along with pilot jets/ mixture screw settings are most noticable under 3000rpm.

[Diskman01]

Ya.. Thats whats throwing me for a loop.. It burbles and loads up at low speeds so it's acting rich. The plugs will blacken up in about 5 minutes of around town driving... If I adjust it leaner it starts really popping.

Choking it at idle makes it speed up. When it's burbling around town, choking it darn near kills it.

Strange..

[bikerphil]

Sounds like a problem that I once had where the PO put stock size pilot jets in but they were the wrong type for our mikuni carbs. Another thing that comes to mind is somthing restricting the air jets in the carb inlet bells with your pod filter setup. Just thinking out loud.

[BA80]

+1 on what bikerphil said. I had the same problem with aftermarket pilot jets.

Some of the aftermarkets have too many air bleed holes, 8 as opposed to 6 on the stock pilots, and it causes that exact problem.

It's actually running lean at part throttle but the plugs get fouled because you have to give it more throttle to compensate for the stumble.

It won't show up on the throttle chop though.

[petejw]

+1 on what bikerphil said. I had the same problem with aftermarket pilot jets.

Some of the aftermarkets have too many air bleed holes, 8 as opposed to 6 on the stock pilots, and it causes that exact problem.

It's actually running lean at part throttle but the plugs get fouled because you have to give it more throttle to compensate for the stumble.

It won't show up on the throttle chop though.

not only did they have extra bleed holes,(which would make it run leaner)
i measured the size of the jet which was closer to 50, way bigger than
the stamped 42.5.

[Diskman01]

I will pull the carbs and check the little air inlets on the input side. I did make the rubber extenders since my pod lips were hosing them up. Maybe the PO did something... Heck, they stuck screws in the sync ports. I splurged and bought rubber CAPS.. No more vac leak there. That was on day 1 this spring..

[James England]

If it's driving you made enough, I would remove the carbs, clean them and renew everything in them using one of Georgefix's kits and use standard jets. Then get the float heights correct.

It seems to me that the problem on older bikes is the PO factor. You just don't know what's been done, or what parts used and so on. Your carbs may indeed have incorrect jets, or mismatched ones, leaking float valves. I know it means expense but, for you guys in the USA it's pretty cheap to buy 4 rebuild kits. If you do the cleaning job etc correctly, then you have a baseline to diagnose from and can say "well, it's not the pilot jets, float valve needles etc". Otherwise you could mess about for ages and go totally insane, trying to diagnose the problem. One good point is that all the plugs do the same thing, so it's possible there are 4 incorrect jets in there. Any PO putting screws in sync ports is capable of messing up the carbs...

[bikerphil]

I will pull the carbs and check the little air inlets on the input side. I did make the rubber extenders since my pod lips were hosing them up.

I have heard of people using the Emgo (restricted lip) type pods with velocity stacks and still having issues. Apparently the filter material itself was restrictive and would choke down the air flow. JAT