Too Much Crack

I have way to much cracking from my exhaust when decelerating on my 84 vf700. I have a Uni foam air filter installed, the needles are shimmed slightly to get rid of the mid-range stumble and I have F1 slip-ons. The entire exhaust system is tight and free of leaks so I have ruled that out. Could it be a screw setting on the lean side? It also does it with the stock exhaust just not as loud or noticeable. I have also gotten rid of the emissions catch bottle to make room for the rear shock reservoir " I have an F4i shock installed". I do have all the PC tubes that led to the bottle capped off with filters Any instruction or advice

 

That sounds like it is running too lean--may need to open the mixture screws a little to richen it up, or clean the pilots jets if they are dirty or go up a size if the mixture screws are at the end of the adjustment range.

It also could be the deceleration enrichment circuit is clogged and not working properly.

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Thanks much, I will try the more simple approach first and try the mixture screws .

 

Please remember one thing.

 

Got it the first time around. I turned in and gently seated the pilot screws and wound up with 2 1/2 turns. I then set them all out to 3 turns. I still have a little popping here and there. Are the screws maxed out at three turns or could I give them a little more than 3. I think I read or saw a video that you should go with a bigger pilot after three turns.

 

No harm in trying more--take them out to 4 or 5 and see if that helps, then bring them back in if that is too much, etc. There is no magic number on the turns, especially if you have made mods to exhaust or intake, just use the screws to tune it how you want it to run.

When the screws are so far out such that no change occurs with additional opening, then yes you will have to go with the next size pilots to get back into an adjustable region for the mixture screw. But you will have to play with it and get a feel for what you need--only you can determine that.

 

Good deal , I'll Give it a go. I 'm sure I'm close. As long as I have your attention I'd like to throw another fuel issue at you. When I ride at a high speed , say 90 or above for a mile two the motor gets what seems to me is fuel starved . I can run at 80 or say even 85 all day and it's fine. It feels like the bike is running out of gas. The fuel filter is new and the carbs were taken apart and cleaned two seasons ago, yes I'm in Wisconsin we have seasons to ride. The fuel pump is working but is there a way to test it to see if it is performing properly?

 

This sounds like another symptom of running lean mixture on the pilots and may be cured by the mixture adjustment also, but here is a way to test.

Put some tape on your handlebar and throttle and mark some lines to easily view and indicate throttle position from closed to wide open, e.g 0, 1/8, 1/4, 3/8, 1/2... Then go ride your test route and report back the throttle positions for when it's running okay ( 60- 85)) and when it's running poorly ( e.g. 90+). This should be on fairly level ground at a steady state speed holding the throttle constant.

 

Opening the idle mix screws more than about 4-5 turns reduces the spring pressure that keeps them from moving, and they'll soon fall out on the road.

 

If you are having fuel starvation problems at high speed, that often indicates that the fuel delivery system can't keep up with the demand. I would check that there aren't any kinks or obstructions in the fuel line, or the tank vent lines.

I ran into this problem with our VFR700. I replaced the fuel line and filter, and thinking I was being clever, I added a couple of extra inches of fuel line to make removing the tank a little easier. Well, the extra line ended up creating a kink. The bike would idle and run fine up to about 30 MPH, then it would go flat as the carbs became fuel starved. It took me about a half a mile of pushing the bike to finally think that it could be a kinked line.

 

I'll get at that sometime this week.

 

Oh yeah, since I turned the pilots out to 3 turns to stop the cracking the choke doesn't work. I have to hold the throttle open to warm it up. after warm up it Idles fine. Is there an adjustment for that also?

 

O.k. I did the the throttle scale and came up with throttle open 7/8 before it started to again what seems like running out of gas. It then takes a good half mile to to catch back up at a slow speed. And during this time it's popping and cracking from the exhaust. I have the pilots turned out to 3 1/4 turns. Am I looking at bigger mains? Right now I have it idling good and it is good around town. I do have #114 mains ordered and I was going to swap the #112 's to the rear. Am I on the right track?

 

It sounds like you have a debris or contamination issue with your fuel system that is causing fuel starvation. It could be rust in the tank, cracked rubber fuel lines or just plain ole dirt and varnish from old gasoline sitting in the bowls. It may be gummy or solid pieces of crud. Why do i think this is the case?

1. Choke was working, now its plugged up (there is no adjustment for the choke).
2. Slow refill of bowl and recovery after high-speed run at 7/8 throttle (sticking inlet valve or floats).

On the other hand it seems that your pilot jets and mixture screws may be working okay-- if they are responding to screw adjustment and the bike runs good and steady without surging at idle, 1/8 and 1/4 throttle.

The larger main jets sounds like a good idea, especially if it is doing this with clean carbs and good fuel delivery system. As long as you are in there to replace the mains, you could also go up one size on the pilot jets to give yourself some additional fuel margin and turn in the mixture screw to set your idle. And of course clean and verify every orifice, jet and port.

You will need to check and verify that all the circuits are clean, and that the fuel delivery system is intact and fully functional from the tank to the bowls and evertthing in between.

You may have a cracked rubber diaphragm in the upper vacuum chamber. This could cause the choke to not function properly plus cause fuel starvation at high revs/throttle opening. These can be checked without removing the carbs. Run the bike with air filter out of the way so you can look down into the carbs and watch that the slides and needles move up and down as you vary the throttle. They should respond and track with the throttle. With the engine off you can reach down with a chop-stick and push the slide up and release it. Should hear some air flow sounds as you move it. You can pull the cover and inspect the diaphragm for splits and pinholes if you are very careful.

 

Well I'm ruling out a dirty fuel system as the tank is spotless inside, looks like brand new metal and the filter is without a spec of dirt or debris , As I am putting in bigger mains I will check everything else you have mentioned. I know the diaphragms were good two years ago but that goes without saying. I replaced the idle jets at the time I cleaned the carbs as they were a little crusted up. I will also replace all fuel lines including the cheap plastic fuel joints with the machined aluminum ones. I'll see what's up this week with the things you mentioned . The bigger pilots I think are are a good Idea . I have the part # 16016-MAH-670 for the oem pilot screws but no info on what size they are so I don't know how to upsize them. I have a factory manual and there is a flow test for the fuel pump. I'll look at that also .Magna Interceptor Sabre V65 V45 V30 Carb Carburetor Remanufacture Service 3 Day | eBay Have you heard of these guys or know of anyone who has tried there service? I've been thinking about going this route also at the end of the season. I

 

Pilot jets are inside the bowl and come in a range of sizes; the pilot or mixture screws are external and only come in one size.

 

I got the 7/8ths throttle issue figured out. I did a flow check on the fuel pump and it was only putting out 10oz. per minute when it should be about 22oz. I ran it gravity feed but had the same problem at near open throttle...fuel starved. Bought a new one from Cheap cycle parts. Putting in bigger mains and #40 pilot jets in the morning. If I need some guidance on tuning I hope you guys will lend some advice.

 

Good catch on finding the root cause to the lean fuel condition. You'll be able to tweak and tune now, and get it like you like it.

 

If it were me, I would give it a try with just the new fuel pump. At less than half recommended flow, you could have been lean throughout the range. It might save you from having to tear them open.

 

Good point, I have run it with the new pump now for hundreds of miles. It is smooth and pulls hard up to redline but the idle seems to be inconsistent from cold starts and the idle hangs for a few seconds when pulling up to a stop. It used to idle up after a few minutes on full choke and now sometimes depending on temp I have to blip the throttle a few times to keep it running from a cold start. I'm going to try and set the pilot screws according to the Honda Factory manual and see if I have any luck.