93 vfr carb issues

Hello, I have posted a few times about my carbs on this bike. Is there anyone out there who considers themselves the absolute "carb pro" for this year of bike and model of carbs. I have had them out cleaned with air and spray, jets out diaphragms checked, floats checked etc. The bike runs well with new plugs and fuel and then slowly goes back to rough idle and losing power. I have huge detals to explain to the right person but the specifics could get rather long winded. Is there anyone who can help me? Thanks

 

Damn wish I could be of some help, sounds like from the read you've gone the distance and no doubt have changed the fuel filter and check the fuel pump. Only thing I'd be doing next is hit up a place that one knows whats what with the VFR and have a dyno tune done. It's how they found my vacuum leak. Good luck, way to nice a bike to be having this sort of hassle, keep at it, it's worth it.

 

Blake:

Where are you located???

(I'm not a carb expert, but this may help)

BZ

 

What the hey? Don't hold back on the detail. Post the specifics. There's a lot of sharp people on this forum.

 

The details

Background: the bike is a 1993 vfr 750f, pearl white, 30,220 miles. I bought it from the original owner in Washington. The bike ran great when I bought it last summer. I rode the hell out of it up until this christmas. One night I let the bike sit with an empty tank of fuel outside when it was 14 degrees outside. DUMB!.... the next day I went to start it. It wouldnt start flooded and fouled the plugs. I put new plugs in it, new fuel and octane then gave it another shot. The bike ran well, slightly better than it did when I bought it. Then after about 45 miles it started to struggle in the mid range and eventually fouled the plugs out again when I tried starting it the next day. SOOOO I tore the carbs out and cleaned them with carb cleaner and air, I DID NOT SOAK THEM. I did take all the jets out that could come out, cleaned them with solvent and air, checked the floats, etc etc, put the mix screws 1 7/8 turns out put new plugs in it and before I put it all back together ran seafoam down through the bores to clean them out. Put it all back together and ran it. It chugged forever with the seafoam and blew a whole bunch of shit out from the valves and pistons ( which I varified because I could see the carbon was cleaned when I looked back into the cylinders etc). Then I put another set of plugs in and the bike ran great. WAY stronger than It ever has, but had a slightly rought idle. Now after about a month and a half of mostly sitting, the bike feels weak again. The fuel is fresh, when I pulled the plugs to look at them the outer ring is carbon fouled slightly. The bike does feel a little rich in the low end. The throttle response is sluggish from idle to 4000 and anywhere from 2000 to 5000 is not completely smooth while riding or just reving in neutral. Does anyone have suggestions for me? What should those mix screws be at? the bike is not jetted, stock filter, and two brothers can. Does anyone know about these carbs and tuning etc? Could the mixture screws make such a difference that in a short time it took a super strong running bike after all the rebuilds and cleaning to a fairly weakened version. Does the plug condition make that much HP difference. To give you an idea I weigh 200 lbs and right after the bike was put back together for the final time and running really nicely I could throttle it hard at about 7000rpm and lift the front tire up, now it doesnt even feel like it pulls hard at any rpm. It runs consistently but is definately lacking. I feel I am a decent mechanic but I am a little lost. Thanks helpers!

 

Okay if you are in WA. State Wet side that is, they are in Bremerton. Give Mike Valsaco a call at Brothers Power Sport. Mike worked for HRC in the good ole days, knows his stuff when it comes to VFR's, 360-479-6943 if anyone would know he would. FWIW sounds like you have a choke issue to me.

 

hmmm...sounds like you've put enough chemicals in it. Proper mixture screw adjustment is important for good idle, but that's not your issue...BTW, My 91 ran excellent at three turns out, it had a two bros can on it also. First thing you might want to do is take a compression test. If there was loose carbon floating around the combustion chamber, it's not improbable that some may be stuck in a valve seat. I've seen this happen on a 600RR recently. I'm not at all sure that's what's going on here, but it would be good to eliminate this possibility before pulling carbs again.

 

I had an old Honda CB360T which did the same thing. Turned out to be a bad coil!!! It would run just fine on a new set of plugs, then slowly begin to run like crap until I changed the plugs again. After the new coil, it ran like a champ for 2 years, until I sold it to buy my first VFR.

 

I am not an expert but do what my Dad has always told me; "start with the most minor item it could be because 90% of the time that is what it is and use common sense, then work up from there". He spent 45 years fixing cars for a franchised dealership and could figure out my junk when nobody else could and it usually was something simple.....

 

Good point Mike...everything makes sense in retrospect...I also wanted to ask some additional questions. Are all four spark plugs fouling? Or is it the same one or two over and over? Is your fuel tank got crap or rust in it...cause it kinda sounds like a float needle might be leaking a bit. I usually inspect the tips of the needles and the seats with a magnifying glass. Did you check the float levels...this is crucial and not obvious on a bank of V4 carbs cause they don't sit level. When you cleaned the carbs, did you find any loose stuff in the float bowls. Did you inspect the slide diaphragms and verify that the air bleed circuits are open to each jet? Cleaning carbs is usually pretty straightforward...ie., a fuel jet is clogged. But on those rare occasions when the clog is in the air circuitry, which will cause a rich mixture, it can get tricky.