Another 'COLD' cylinder-- #4

[MarkD]

Hi everyone. I'm having the same issue I had last Fall. If you can reference my post; ( Cylinder #1 is 'cold' - Help!), I and having exactly the same issue, except it's a different cylinder. Same checks this time, I even used a spark tester, and the firing is as strong as the other cylinders. I pulled and cleaned them 2X so far, with a complete teardown, even using compressed air. I am really frustrated at this point. Pilot jet issue? I did cover the kidney shaped air Venturi? inlet, and the revs increase right away. I covered the other 3, and the engine starts to lose revs, and nearly stalls. So, covering the problem cylinder does a different thing to the engine. All help appreciated!!

[DEEBS11]

Sounds like a possible air leak but certainly a lean condition. Maybe a clogged jet. Maybe a manifold problem. When you cover the air inlet, you are introducing more fuel into the cylinder. The other cylinders don't like it because they are already getting the correct fuel/air mixture.

[MarkD]

I just pulled the carb off the rack-- research says a good boil in Pine-Sol might free up some crud. Hard for me to believe any crud could be in there, since I cleaned 2X, but at this point it's worth a boil. Thanks, Deeb, I'll also recheck vacuum tubes, etc.

[bikerphil]

You could try opening (turn out) the idle mixture screw a bit and see if the pipe warms up.

[MarkD]

I'll give that a try, Phil. Thanks.Totally disassembled carb is soaking in Pine-Sol right now. Reassembly starts tomorrow.

[LAB3]

I've had mixed results with pine Sol. One thing I did figure out with it was at least one hour on a boil then let them soak for the next 24 hours after that. The first time I tried it I didn't let them soak very long and my bike (Suzuki GS450) ran "good enough" but letting them sit longer did the trick. Actually, a second boil after the soak might not be a bad idea either.

[MarkD]

Thanks, LAB, I have them soaking now, will reheat the stew, and let soak another day.

[Radioguylogs]

Double boil, toil, and no trouble?

(Shakespeare)

[MarkD]

I'll find out! Hopefully it's all good.

[gtem]

I like to check for air leaks on a idling bike by "sniffing around" with an unlit butane torch to see if revs go up when the torch nozzle is brought up to intake boots etc. My gut feeling would be a clogged pilot jet. After your soak, I'd make sure to actually test the pilot circuits by spraying/pressurizing WD40/compressed air through the passages and make sure you see flow through all the little orifices at the carb bore.

[MarkD]

That's my next step, Thanks, GTEM.

[Schming]

Quote from Biker Phil;

"As for the enricher circuit, make sure this passage is clear in the bowl. There is a tiny jet down in there, shine a flashlight thru one hole and to verify it's clear after cleaning..."

[cajun31]

I'll give that a try, Phil. Thanks.Totally disassembled carb is soaking in Pine-Sol right now. Reassembly starts tomorrow.

Mark, I am not promoting Autozone. Just they have this product. You would be much better off soaking those carbs in this. Berryman Chem-Dip Carburetor and Parts Cleaner 96oz

The gallon can version of this is safe on rubber parts. They also sell a 5 gallon version but the chemical makeup is different and will damage rubber parts. You stated you disassembled your carbs. Have you ever pulled the butterfly shafts to check the conditions of your shaft seals. I also replace those when I rebuild/clean carb banks. Learned a long time ago that until you do a very thorough cleaning by totally disassembling the carbs you will chase your tail. These old vacuum carbs are finicky and until you get them clean and dialed in will make you crazy. I had a problem with a set one time with the same problem you are describing. Until I actually replaced the pilot jet with a new one the problem just would not go away and believe me I had cleaned everything and checked every orifice with a flashlight. I always take those small parts and put them in my ultrasound cleaner with white vinegar. I heat everything while running the ultrasound. I can actually see crude coming off and out of them. The Berryman really cleans those passages you can't see. I always blow air through everything after taking them from the Berryman's to hot water then air making sure all passages are clear.

[MarkD]

Thanks, Schming and Cajun. I have an update. After boiling the carb and pieces, and a thorough hot water rinse, I blew all the jet openings and orifices, including the passage in the float bowl bottom. I did not take the butterfly out, hence, I didn't see how the seals are. Anyway, upon reassembly and install, I started the old girl up, and guess what, #4 cylinder is hot and strong! I have had issues with carbs before, but this one got to me, but with all you guys helping with tips and info, it didn't beat me. This forum is great. The archived posts are a great help as well. The seal safe Berryman's is what I'll use next time I need a complete soak, as the Pine- Sol did need a heavy rinse, too much of a pain to deal with next time. Glad this story has a happy ending, Thanks to all, and Happy Thanksgiving.

[LAB3]

One of the things I learned about using PineSol is that you need to use deionized water to rinse them or the metal will darken. No big deal for me but someone doing a pristine restore would be put off by that