1999 BF90A “NO IDLE” and Gasket Question

Struggling with the dreaded “no idle issue”……
Removed/cleaned/rebuilt the carbs. Used all new Honda gaskets.
Unfortunately ……still no idle …..unless the idle mix screws run way out and choked.
Removed carbs again….(groan). Noted the gaskets were all intact, not stuck to any surface anywhere.
Has anyone had any problems with Honda gaskets not sealing? Bolts and screws were torqued appropriately.

Unless gaskets didn’t seal, I don’t see any other sources for too much air. Seems there must be something still blocking fuel although everything seemed pretty clean on assembly. Inspected every little hole in jets and tubes. Have ordered an ultrasonic cleaner to really blast the carb bodies and all parts before reassembly. Hopefully that will clear any blockages.

Would you recommend using ew gaskets even if these are “basically new”? Getting quite expert at removing/reinstalling Honda carbs, but really don’t want to do this again!

Despite being over 20 years old, this motor is very clean and had been running beautifully. Any assistance in getting it squared away will be greatly appreciated. Thanks!

The ultrasonic cleaner will help... I suggest that you put the carbs through the U-cleaner 6-7 times.

Any other trouble shooting done ?----Did problem show up suddenly ?

Because you're running the idle adjustment all the way out, my bet is you've missed the most important jet when cleaning. It's hiding inside the brass tube that runs vertically through the center of the carb. This jet is not much bigger than a whisker hair and has caused more trouble than all other carb problems combined. The acid test is you need to be able to see through the length of that tube. You're going to need your glasses for sure, or maybe even a younger set of eyes. It's difficult to see through even when right. If that jet is positively confirmed open, there's 2 more places to look for the answer to this issue. They're both tiny o-rings (the ones that come in the gasket kit). The one at the top of this same vertical brass tube, and the one on the idle mixture screw. Both of these must seal in order for the engine's vacuum to pull fuel from the float bowl to the top of the carb where the idle jets reside. Worth noting, I've been doing these for a while now, have done a countless number of them, and I STILL have to pull a set back down occasionally to redo them. Not as often as when I first started, but often enough where I still hold my breath until the engine settles down into the idle I know it's capable of. -Al

I use hylomar ultra blue on both sides of any gaskets I install, it never hardens, it usually means you can remove the gaskets and reuse them. It is not and RTV so doesn’t clog things. It was developed by Rolls Royce for jet engines. I had an Evinrude I was working on and when I ordered it, it came with a small tube of it.

I use only grease. If the surfaces the gaskets seal on are clean, they don't really need a sealant. I use grease so I can re-use the gaskets a few times. Like for those instances where I nee to re-do the carbs. The grease prevents the gaskets from sticking - a trick dating back to when shirt pockets hadn't been invented yet.

Thanks to all for the replies. I did try to pay good attention to the slow jet emulsion tubes…all the tiny holes did show light.
Almost tempted to just buy new, but would push $90 for the four. The O rings were all new.
Hopefully the ultrasound will do the trick. Seemed that Simple Green was the popular solution to use. Any suggestions here?
As far as other troubleshooting….just checked and adjusted valves. New filters. Fresh gas (always non ethanol).
Appreciate the help. I’ll keep fingers crossed, but can’t hold my breath that long!

Lunasea said:

Thanks to all for the replies. I did try to pay good attention to the slow jet emulsion tubes…all the tiny holes did show light. Almost tempted to just buy new, but would push $90 for the four. The O rings were all new. Hopefully the ultrasound will do the trick. Seemed that Simple Green was the popular solution to use. Any suggestions here? As far as other troubleshooting….just checked and adjusted valves. New filters. Fresh gas (always non ethanol). Appreciate the help. I’ll keep fingers crossed, but can’t hold my breath that long!

Click to expand...

Regarding the "tiny holes", were these in the sides of the tube, or the bore? The one in the bore is the important one - that's overlooked most often.... worth checking again if you aren't absolutely sure.

Point well taken. I will certainly check bores before reinstalling. May need to bite the bullet on new if not thoroughly convinced they are clear after ultrasonic cleaning. Do you have a favorite cleaning solution? Machine arrived this evening and I will crank it up tomorrow morning using Simple Green unless you have a better recommendation.
Thanks again for the help!

BTW….Chris mentioned putting carbs through 6 cycles. How much time per cycle are we talking?

I use an "old school" (poor boy) approach. It's carb cleaner and compressed air. There's a lot of talk about replacing these tubes, but it's something I've only done on rare occasions. If/when I run across an idle jet I can't clear with carb cleaner and compressed air, I use 1 wire bristle pulled from one of those dollar parts cleaning brushes. I clamp it in a pair of needle nose vice grips so I don't loose it, then straighten it. Works perfectly. Do not try to use a bristle from a larger wire brush - they're too big! -Al

Hi,
How much attention did you give to the low speed air jet? Those air passages often get overlooked because people don't realize they're there.
There are two passages at the front of the carb on the flange above the main air channel. They provide the air velocity for the low speed and high speed circuits to extract fuel from the float chamber. Deep inside them are air jets (restrictions) that can be blocked. Just another area besides the jet set tube and carb throat orifices that need extra special scrutiny.

I have a couple of ultrasonic cleaners but find carb spray more effective at cleaning these little finicky carburetors.

Just my opinion.

Good luck.

Has anybody checked other areas such as camshaft timing ,timing gear to camshaft align, or timing belt timing

Anything is possible, but I've never been able to justify the time with the results I've had. In my experience, Honda has a rock solid cam timing setup.

Well, some follow up…..
The ultrasonic cleaning made a distinct difference. Nice looking parts…seemingly better than the carb cleaner results. Allowed for very detailed inspection.
I did find the tiny “ inline” jet in two tubes still blocked. Managed to clear with some fine wire.
Also found what might be very faint hairlines that might be splits (or simply scratches?) on two tubes at the end opposite the O ring. Tubes don’t seem distorted, but if indeed splits, I figure I am going to have to replace. Sure don’t want to pull everything back apart! Not sure why tubes would split….. If anyone has any thoughts on these possible ‘splits’, please let me know.
I did pay attention to those two passages. Thanks for the heads up. Passed fluorocarbon line through the hidden jets.
I used carb spray liberally on first and second cleanings. While the US seemed to take off even more, I will shoot spray through everything again before reassembly. At this point, I don’t feel there is any “above and beyond” if it keeps me from doing all this again.
Thanks again for all the help.

2 still plugged SO typical! No idea on why or how, but if those are cracked, it wouldn't be the first time.

Those tubes are NOTORIOUS for splitting/cracking. I have always thought that it was because they are under compression from the plug that holds them in place from the bottom. But it could just be vibration. I can't say for sure but I saw many that were split.

That and the fact they are so hard to get clean makes me "one of those" that Alan references that advocates just replacing them.

But...I only worked on twin engines so it was just one at a time and the cost was low. Wasn't worth my time to "futz" with one.

Sounds like you're getting closer.