Topic: 77 CB550F - Rpm rises high when disabling choke

[DeLuxe]

I bought the bike not running; it had sat for 10 years.

I changed the oil, gas, and replaced all the tubes.

I cleaned and rebuilt the carbs according to specifications.

I also replaced the rubber boots.

When I disable the choke, the RPMs increase a lot. The idle screw is turned out quite far. It sounds fine when the choke is on, but I can't get the choke halfway off.

I even tried a pod filter setup, but no difference.

I also did check the throttle, but it works as intended.

Any ideas/suggestions?

[RAFster122s]

Clogged jets in carbs, pilot idle jet

[DeLuxe]

I'll try doing an ultrasonic cleaning, I only did carb cleaner with compressed air. I hope that is the issue.

[M 750K6]

Throttle cable adjustment, or sticking?

[DeLuxe]

Alright, I did an extensive cleaning on the carbs...

30 minute berryman chem dip per carb body and float bowl
15 minute ultrasonic with carb cleaning solution per carb body and float bowl

The jets themselves are stock sizing and they're all new.

the issue is still persisting...

I have it on camera, first time starting after putting carbs back on...

Youtube Video Showcasing Issue

[newday777]

Did you buy carb rebuild kits and rubber boots from 4into1.com?
Did you remove and clean the original brass parts, jets, from the carbs or stick in brass from the kits? Who's kits??

[DeLuxe]

Did you buy carb rebuild kits and rubber boots from 4into1.com?
Did you remove and clean the original brass parts, jets, from the carbs or stick in brass from the kits? Who's kits??

I used 4into1 for boots and rebuild kit.

I removed all brass before dipping the carb bodies. I reassembled using the kits new parts.

Is it possible that the timing is too advanced? I'm going to check that next chance.

[newday777]

4into1 sells junk Chinese crap. The rubbers don't seal and cause vacuum leaks and poor running.
The brass in the kits are not made properly and are a tuning nightmare.

[Stev-o]

+1...aftermarket jets are crap, get genuine Keihin brass.

[HondaMan]

At the very least: go back to the original jets and brass parts. Do NOT use jets and parts from 4into1 or anything made by Keyster or K&L for this bike. They will all act as you're describing.

Today, "rebuild kits" for the SOHC4 bikes are virtually non-existant in a correct form. Only those kits that are rubber-only pieces are really needed: Honda still supplies those for the 550 bikes, for the most part. The brass parts do not ever wear, so re-use the original ones.

The intake runner hoses between carbs and intake manifolds don't usually 'wear out', but the O-rings in those intake manifolds, where they bolt onto the head, are hard as a rock and don't seal unless you have changed them. They are the same size as those in the valve caps. If you removed those manifolds and did not change the O-rings on re-install, they leak - bet on it.

[RAFster122s]

The rubber hoses for the intake harden and often don't seal after the carbs have been off after they are decades old has been my experience. I tried softening a set with wintergreen oil and other than swelling too much and getting soft they quickly hardened back up after the wintergreen evaporated. New ones from Honda are the way to go, the aftermarket ones have a reputation of failing within a year...

[Deltarider]

The rubber hoses for the intake harden and often don't seal after the carbs have been off after they are decades old. New ones from Honda are the way to go, the aftermarket ones have a reputation of failing within a year...

My new OEM boots are still in their plastic bags. Although my boots are on the bike since 1976, I have no indication of leaks. At idle it would become manifest. I favour diagnoses over assumptions.

[jonda500]

I don't personally know what rubber boots from 4into1 are like, probably not the cause of your problem, but I agree with Deltarider and Hondaman - original boots don't wear out or go bad, only you may need to warm them and lube them if they are too hard to get on/off.

When you re-assembled the carbs, how did you sync the slides -it's possible to set them too high so they can't return down far enough to idle?
John

[DeLuxe]

I could never figure out the issue with the original carbs. I caved and just built an intake manifold and got two Mikuni VM34 carburetors. The bike runs amazing now, just thought I'd post an update!

[Stev-o]

I could never figure out the issue with the original carbs. I caved and just built an intake manifold and got two Mikuni VM34 carburetors. The bike runs amazing now, just thought I'd post an update!

Thx for posting your update, we've had reports that the Mikuni carb mod does not always work out

[kerryb]

Hey deluxe, would you like to sell the original jets you took out?  How about the carb bank with the old jets?

[DeLuxe]

Thx for posting your update, we've had reports that the Mikuni carb mod does not always work out

Yeah, it took a lot of tuning and testing. I finally have a good enough configuration. I wouldn't recommend it to someone who doesn't know how to tune carburetors.

[HondaMan]

Thx for posting your update, we've had reports that the Mikuni carb mod does not always work out

Yeah, it took a lot of tuning and testing. I finally have a good enough configuration. I wouldn't recommend it to someone who doesn't know how to tune carburetors.

I'm glad you could figure that one out: I've had quite a few inquiries about it, but as I've not done one, I don't have much to say about other than this: that's quite the cavern inside those intakes! I would think the idle part would be hard to figure out.