Honda bf90 backfire

[n628ms]

I have a 1998 bf90 that backfires through the carbs when you accelerate. Rebuilt the carbs with no success. Clean fuel and filter.
Any suggestions?

 

[JUSTINTIME]

Re: Honda bf90 backfire

timing is off

 

[n628ms]

Re: Honda bf90 backfire

Thanks for the reply. I would have thought the same thing but the manual says that the timing can't be adjusted.

 

[JUSTINTIME]

Re: Honda bf90 backfire

i have seen the belts skip a tooth

 

[n628ms]

Re: Honda bf90 backfire

The marks on the crank and camshaft line up properly. Is there an adjustment on the electronic pick-up?

 

[n628ms]

Re: Honda bf90 backfire

I did another test run and when I accelerate it bogs down. If I choke it real quick it picks up then dies off again. I tried to set the pilot screws for a richer setting but did not notice an improvement.

 

[Sea Dawg]

Re: Honda bf90 backfire

Your last post feels like deja vue. I just bought a used 98 BF90 and currently am going through the same scenario. The motor doesn't want to turn over so I hit the choke only for it to turn over and slowly die; it never holds idle. The previous owner had fuel issues as he predominently used ethanol. So I assumed there was a lamination / gumming up issue so I dumped all the old fuel and replaced the fuel filter only to be at sqaure one with the idle issue. Were you able to get your issue resolved? I'm curious if it was a timing issue If so what was your solution, I may be in the same boat; no pun intended.

 

[n628ms]

Re: Honda bf90 backfire

It idles great. It only bogs down when you accelerate and it backfires. If you rev it up slowly it does not backfire unless it is under load. I still think it is carb related.

 

[psteurer]

Re: Honda bf90 backfire

We have two posts going on for a BF90. Both appear to carburetor related. For the first post from n628ms, did you synch the carburetors after your rebuild? If not, that could be causing this problem. For the second post from Sea Dawg, sounds like your carburetors are clogged. Old fuel sitting in the carburetor will clog the tiny ports where the fuel passes. From your post, it sounds like your idle circuit has the problem but it could be elsewhere as well. For preventative maintenance, it is advised that you drain the carburetors of fuel if you plan to let the motor sit for more than 2-3 weeks. Also, run some fuel stabilizer in your gas.

 

[n628ms]

Re: Honda bf90 backfire

Today I sync'd the carbs. It ran a little better but still backfires through the carbs. A local guy told me that the low speed jet tubes might be cracked. He says that it happens alot on Honda's. Also, has anyone heard of this problem being caused by bad valve guides?

 

[JUSTINTIME]

Re: Honda bf90 backfire

is it sneezing or back fire

 

[n628ms]

Re: Honda bf90 backfire

I guess it would be sneezing. I don't actually see any fire.

 

[JUSTINTIME]

Re: Honda bf90 backfire

pull the carbs off

you need to remove the 2 jets and the pilot tube

use an ultrasonic cleaner

then use a fine brass wire to ream the inside

 

[n628ms]

Re: Honda bf90 backfire

o.k.. I cleaned the jets as you suggested even though they looked really clean. Put everything back together and it still sneezes out the carb. Is there any chance that the valve guides are bad? I am getting the for sale sign ready. Haha

 

[JUSTINTIME]

Re: Honda bf90 backfire

did you remove all the parts in vcarb

 

[n628ms]

Re: Honda bf90 backfire

did you remove all the parts in vcarb

Everything I could remove I removed. I even blew out all the passages with an air hose. Everything appears clean. I asked a local Honda mechanic if he thought it could be valve guides or springs and he said he has never had to rebuild a head that wasn't caused by overheating.

 

[hondon]

Re: Honda bf90 backfire

Has anything been done with the accellerator pump side of that manifold?A leaking diaphram or stuck check valve could cause your exact problem.Keep in mind that these engine were designed as utilitarian and really do'nt like to be stood on,but if its acting differently than you are used to you might consider looking at that pump assembly.

 

[Wheelhouse]

Re: Honda bf90 backfire

It sounds like you have a vacuum leak on the engine side of the throttle plates. When the engine bogs down will it pickup if you choke it? Choking it makes the fuel mixture richer. With the engine at idle, spray some WD40 around the Carb bases and where the manifold connects to the head. If you have a leak the vacuum will suck the WD40 in.