1986 VFR750 Carb help

1st of all... WTF? Never heard of that.

Just order by part number. They don't know what bike you are ordering for.

99101-MBZ-1250 (disregard)
99103-MV9-0420 - Used on VT1100 Shadows and XR250R

Like I said in a previous post, just take the VFR part numbers and change to the size you need. Just did this about 3 months ago.

Edit:. Actually, sorry. Main jet part number not working. I guess I already had the jets. But I did do it for the pilot jets. That one works.

Edit again:. Main jet part number 99101-443-1250 (Used in 1994 VFR750F)
Got this part number by taking original Honda part number (not the superceded) for the 1986 VFR main jet and changing it to 125, it then updated to this part number.

 

With Mikuni main jets, I believe that there are different style of Main Jets, depending on type/year of Manufacture. Keihin is the same, or the Dude behind the counter has different ones and wants to be sure. Either take one with you, a picture of your jet, or just be able to identify it, for sure!
After being on this site for a while now, I'd fully trust Captain 80's advice. Squirrelman as well. I was recently cleaning carbs on my 1987 Honda VFR700F2 but after I was very "Confident" that I did all that was needed and reassembled my carbs I had poor top end. Another session cleaning got my top end back. Download a free service manual, from Honda, then follow ALL steps suggested by the people here and in the manual. You'll then have a proper running bike! Hopefully! (Check yer tank vent!)

 

have everything apart (again) and will double check that all journals are clean and install the new jets (assuming I can find them today) and see how she goes. Will just be happy to have everything sorted once and for all. It is tough when you get something with no history on it but I will get it all sorted.

Thanks again for all the help.

 

Ok, well - I figured I would post an update (not so much for you experts but more for the newbies like me).

I broke everything down again and I cannot believe how much faster and easier pulling the carbs are now as opposed to the first time I tried it so I guess the old saying is true "repetition is the mother of skill". I prefer the ratcheting tie down trick and seem to seat them very quickly using that method.

Anyway here is where I am at so far. I could only find a set of 126 mains but I figured that is close enough to where I wanted to start and used 42 pilots. I double-checked everything which all looks clear and backed my mixture screws to 1 and 3/4 turns out for a starting point. Took the bike out today and as usual, there is not a day that I am out where someone does not come up and recall back in the day when this bike first came out. It brings so much nostalgia out of people it is amazing.

As for the performance eval, I now have great top-end (at least more than I can test on the roads available to me) but I now have a "sputter" in the 1/4 to 1/2 throttle range and the roll from a stop seems to be a little rich so I pulled everything apart again and decided to remove the 0.20 shims I put under the needles and backed my mixtures to the bottom of the effective range (1 turn out) and took her down the street and miraculously the bike seems to run perfect. Not flat spots or strange transitions but I will need to hit the canyon tomorrow to confirm but this is the best it has ever run.

I guess one thing I learned out of this (so far) is that something as small as a 0.20 shim makes a huge difference in how the bike runs. I am not sure how much bringing the mixture screws in 3/4 of a turn did for me but I believe I may be done and can just enjoy the bike now. I will confirm tomorrow but wanted to take a minute and thank everyone for the input. I had absolutely no reference point as to where to start on this bike and I am tempted to let the previous owner ride it now to show him what a difference there is in the power delivery but this may make him want it back so maybe I wont do that

Still amazes me that the previous owner(s) opened up the airbox and put the 4/1 exhaust without doing anything to correct the jetting so if you pick up a bike, don't always assume they knew what they were doing and check everything.

Oh, and just to top off my family curse my damn choke cable broke. Fortunately when I went up to the 42 pilots it seems to start pretty well without even using the choke so it may not be an emergency to find the replacement. Anyone have a source or part # to replace that?

Thanks again guys. 126 mains an 42 pilots with the mixtures out one turn and no needle shims seems to be right in the ball park for this bike. Maybe I will fine-tune it later if I get really picky but from tonights test run down the street I would have to say it is pretty close to perfect - fingers crossed it will behave the same tomorrow in the heat...

 

Thanks for sharing the "after" report--we don't always get those and it will help the next guy somewhere down the road.

When i read about the 1/4 throttle and off the line response i figured it was running too rich and the 42 pilots were too big, but you were able to negate it with the screws. i'm thinking at 3/4-1T you probably have no flow thru the mixture port but it's actually pulling thru the transfer ports.

Another approach would be to use the 38s and open the screws wider, or use 40s with the screws at midpoint. With the screws nearly shutdown you have little to no adjustment e.g. for riding at different elevations, mountains vs sea-level, etc.

Personally i would rather use an adjustment screw to add more rather than trying to use it to throttle something back--you can always open it more, but can only close it so far, so more range is available for tweaking and fine tuning.

Put a couple hundred miles on it and check the plugs--i'll bet a pint of barley pop that they will be black and sooty. Keep a record of your fuel mileage just to compare with stock configuration.

Most slab riding is done with only partially-open throttle running off the pilots, and that will affect fuel mileage greatly. May not matter in your case, but it might for someone who is commuting.

 

Well, I had another hot day to get some miles on the bike and I have to say it is almost perfect. My only real issue is that I do not have any reference as to the potential of the bike. I am used to a modern FI liter bike so it will probably never be as fast as I like but as far as the jetting is concerned it is now very smooth through all transitions and pulls nice on the top end. If I had to go out on a limb, I would say that the bike could still use more fuel on the top end and I may need to bring my mixture screws out 1/4 turn as I have some very mild popping on decel but it is very mild and almost not noticeable.

I still am little amazed that everything came together so nicely and fully expected to be chasing flat spots or at the very least transition issues but it is flawless. I do have bit of a drone at WOT from the air box mod (holes drilled in it) but I expected to hear something when it has been opened up like that.

Looks like I hit the sweet spot or at least very close and maybe I will go for a Dyno run to confirm down the road. I ordered a carbtune manometer so I will take a look to see how close they carbs are when I get that.

Thanks again for all your help guys, I love the bike now and decided to keep it since it is so much fun.

 

Good news.

 

[thread revival]

I got the bike running very well and have really enjoyed riding the bike but recently ran into another carb issue so I thought I would keep this thread going...

Came out to start the bike and starter moved for a second then bound up, my first thought was the starter or battery but soon realized I have a very strong smell of gas so it looks like I have a cylinder hydro-locked with gasoline. I am fortunate that it did not fire so I shouldn't have to worry about physical damage. I pulled the oil plug and smelled the oil and sure enough I have a strong gas smell so it looks like I have another adventure ahead of me.

So... Is this a common issue with these older bikes? I assume I will need to replace a float needle (or likely all of them given their age) and drain the oil and refill with fresh oil.

I am not looking forward to tearing everything down again as this will be my 6th/7th time after my last jetting adventure but I guess repetition is the mother of skill so as the old saying goes "don't chew on the turd, swallow it"...so I am getting ready to get to it.

I welcome any comments/tips/shortcuts and plan to tear her down this weekend.

 

If a float sticks open doesn't the fuel just feed into the overflow pipe and not into the inlet tract/cylinder?
I used to have a sticky float valve on a GS1000 and a smart tap with the handle of a hammer would free it up.

 

well, I picked up some float valves and was amazed how expensive they are. The parts counter wants $48/ea. for them. Not sure why I can see $5.00 ones on ebay or $50 ones from the manufacturer but I certainly don't want to have to do this again so I got the expensive ones. I am confident I have a problem with only one of them but given that they are 30 years old I decided to replace them all. Who knows? Maybe I will get lucky and not have to take the thing apart for the 8th time...

Anyway will report back once I get in there to see what happened...

 

Very common problem on bikes of its age.

Fuel could get in through a leaky needle AND an open valve. It's always best to bench test the carbs with gas b4 mounting up 'em bitches, and i usually wait up to 24 hours to check for float bowl, fuel joint, or needle leaks, easy to locate with carbs on cardboard.

 

So you were the feckless bloke on the GS forum looking for a replacement float bowl cover ?

:witless:

 

Never bust them. Stopped the leak. Cheap solution. I was poor. I had no option.

 

Well, I tore into the bike this weekend and have a little information that I can add. When I went through my carbs after getting the bike, I did not remove the float needle seats and now with my latest hydrolock situation I now realize that there are little filters behind them. I replaced all four of the float needles with the Honda kit that includes a new float needle, seat, filter and crush washer and while I was in there I tried to inspect my old needles in comparison and even under strong magnification I could not see anything that would flag a failure so I am not sure what happened but what I did notice was how much crap there was on in and around the needle filters. It was so bad I essentially had to reclean the carbs.

So, if you are new like me - when you clean your carbs be sure to remove the float needle seats and the filter behind them to clean your carbs correctly. I am sure this is old news to the veterans in the group but I have read many posts on reviving an older model bike like this after sitting for long periods of time and cannot remember one instance where anyone talked about these micro filters.

Anyway, this turned into a weekend of maintenance so I rebuilt my clutch slave cylinder (was surprised how bad that was), replaced my broken choke cable, installed a new LED headlight, changed the oil and fixed the carbs. I was already happy with how my latest jetting change (went with 42 pilots and 126 mains) went but the bike runs even better now. It is a nice surprise as I just wanted to get it back on the street and thought I already had it running well but it is absolutely perfect now. I cant imagine how it can run any better.

...getting ready for a canyon run today so I hope this helps any other newbies that might be chasing down carb issues. I am not sure what the deal was with the hydrolocking, just happy it didn't fire and break anything. I now turn the petcock off when it is going to sit for any extended periods of time.