Surging @4000 rpm

[Hime696]

I have just bought a 86 Vmax. It was sitting for 2 years. It has 12,000 miles. It is stock except for a k&n air filter. The carbs were overflowing fuel out of the vents when I first tried to start it. I took the carbs apart, inspected & cleaned them. checked float level: level is correct (I have read almost all of the carb tuning threads). I performed the "shotgun" and the "pea shooter" methods.
The bike idles good. But, it will surge @4000 rpm, most notable in 5th gear. It feels like is running out of fuel. But if I go to WOT, it will hesitate slightly and then accel hard to redline. I have the mixture screws 4 1/4 turns out. It seams to not surge as much then having them @3 3/4. If I accel from about 2-3k rpm, it pulls right to redline, hard. I'm not sure if I missing something. Any ideas?

 

[COP RUNNER]

SEND , maleko89 A PRIVATE MESSAGE , HE'S THE CARB . SPECIALEST!unk:

 

[82ndCowboy]

IF it's stock, Vboost should kick in at 6000 rpms. You should feel a kick in the pants as your accelerating at 6000 rpms.
Normally the needles don't have to be out that far.
Have you checked ALL the rubber boots around the carbs and intake for cracks and dry rot?
Also check your gas tank to make sure there isn't all kinds of rust and crap in there.
Check your fuel filter?
And Did the previous owner modify or remove the Y on the top of the air box?
I would also check the condition of your fuel lines. Older lines and new ethanol levels in Gas don't seem to be playing nice together.

Hope that gets you started.
More of the guys will add more I'm sure.

 

[dannymax]

Did you sync the carbs after doing all this work?

 

[Hime696]

Other things I left out: I replaced the fuel filter & synched the carbs. I do feel the Vboost kick in @6000 rpm. I placed the small washer as a spacer in the needle jets and it was still the same.
The"Y" is stil intacted on the airbox.
If there was a vacuum leak in the rubber intake boots, wouldn't the idle be rough(lean misfire)? I'll check that tomorrow.

 

[82ndCowboy]

Other things I left out: I replaced the fuel filter & synched the carbs. I do feel the Vboost kick in @6000 rpm. I placed the small washer as a spacer in the needle jets and it was still the same.
The"Y" is stil intacted on the airbox.
If there was a vacuum leak in the rubber intake boots, wouldn't the idle be rough(lean misfire)? I'll check that tomorrow.

If it's a small crack it might not leak until the velocity is increased, therefore causing issues at higher rpms.

 

[gleno]

Air, fuel, spark.

It sounds like a vacuum leak.

Have you checked to see if the rubber caps that fit over the vacuum tube inlets on the lower manifold (the ones you pull off the attach the carb synching tool) are sealing correctly.

Are the lower manifolds tight on the heads?

Is the rubber hose to the vacuum sensor leaking?

Are all the rubber manifold connections correctly clamped and sealed?

If they are fine check for a big fat spark at each of your plugs.

If it's not fat at any cylinder, then check your plug lead connections.

Air, fuel, spark.

 

[naughtyG]

I also had one night only of my Max feeling like it was fuel starved - hesitating and surging all the time on the highway, but only when cruising at 4-5k rpm. It was fine on idle, and accelerated fine too. Then the next time I was on the highway it was fine, and I didn't do anything to it, other than filling it up again..

So I reckon I just got a tankful of shit gas, as it's the only explanation that made sense to me. Do you remember where you filled up last? Do you always go to the same station or change every time?

 

[lankeeyankee]

SEND , maleko89 A PRIVATE MESSAGE , HE'S THE CARB . SPECIALEST!unk:

Mark is busy flipping burritos for me..:nyah nyah:

Hmm floats were stuck,, just for shits and giggles did you replace the spark plugs, its simple and at 2.50 a piece I am sure they could use some new ones after sitting so long.. Start with the simple stuff first..

 

[Hime696]

Thanks for all of the replies. I'm going to check the intake system below the carbs this weekend.
Has anyone used a smoke machine on the Vmax to check for vacuum leaks?
Thanks,
Jim

 

[hubeerjw]

Another thing you might want to check is your needles. There is that white plastic washer with a small tit off of one side. Pull your slides/needles out and double check that that tit is set in the hole in the slide. When I put Morleys carb kit on, I thought I had them seated properly, but when I went to check them 3 were not in correctly and I had the surge you were talking about. It would idle perfectly and at WOT it would scream, but driving around town was a different story. It sounds like you are too rich in the mid range.

Jeff

 

[Hime696]

Update: I checked for a vacuum leak- none found. One thing I'm not sure of. The carb vent hoses for the front cylinders feed down behind the rear of the engine. The rear carbs don't have hoses on them. Now there are 2 nipples on each side of the air box. Are the carb bowl vent hoses suppose to attach here? Does the carbs need the bowls to have the same incoming air "pressure" as the air box(like carburated bikes with ram air)?

 

[Storloc]

If I understand which hoses you are referring to they belong up top. I attached a couple pics to show how they are mounted from the factory.

 

[naughtyG]

:confused2: My '86 is also suffering from the same hesitation/surge problem, although for me it's anywhere between 4ooo and 5ooo rpm, and only while cruising.

By that I mean that if I'm accelerating, WOT or less no difference, the bike goes right through the 4-5k range without problems. If I cruise below 4k, I have no problem. If I cruise at 5.5k or above, I don't notice anything wrong either. But try cruising anywhere between 4k and 5k, and there it is.
Also, I found that this problem is also intermittent :ummm: Last night I got on the highway and everything was fine for the first 20-30 miles. Then it started again - right in my usual cruising rpm range - as I sustained 4-4500 rpm, the bike would feel fuel starved and keep hesitating then surging again, randomly but all the time. As I rode to work this morning it seemed fine again.

Also, yesterday my bike got the rough idle trouble again. It ran fine while moving, but whenever I would come to a stop I would have to blip the throttle to keep it running or it would die. It would be hard to restart too, often needing choke to get going again.

So I performed the shotgun - I'd only just done it about 2-3 weeks ago to cure the same problem.

No shit came out of the fuel bowls, and the A/F screws came out clean and are in good condition. Doing the shotgun I saw no dirt anywhere, but upon completion it idled ok again.

All my A/F screws are set between 2 and 2 1/4 turns out. Rubber boots are tight and look in good condition. All 4 vent hoses are in place. Y is unmodified, air filter is looking good. Fuel tank is clean inside, fuel filter looks good too. I checked spark plugs and they all look fine and are gapped properly. Yesterday I also topped up my battery and gave it a good charge.

Since doing the shotgun for the second time, the bike idles ok again, but it's not totally smooth: it seems to drop/skip intermittently, and this gets worse the longer I leave it idling.

Has anyone got any clue about what could be going on? :ummm::ummm::ummm:

 

[maleko89]

4-5K is transition from pilot mixture to needle. Slides on a stock bike start to open at 4500 rpms. You can try either dropping the size of PAJ2 a size or two or you can shim your needles a tad.

 

[naughtyG]

4-5K is transition from pilot mixture to needle. Slides on a stock bike start to open at 4500 rpms. You can try either dropping the size of PAJ2 a size or two or you can shim your needles a tad.

That's real good info Mark! My needles were actually shimmed when I got the bike, and I removed the shims in an attempt to go more stock to better my mpg as it's on the low side. I shall put these back in and see if it helps.

I had a good look at PAJ 1&2 yesterday while doing the shotgun, and from memory I think they are 90 and 170.

What about my rough idling problem? Would downsizing PAJ2 help with this? 2 x shotgun in as many weeks seems weird - especially since everything's clean. As previously mentioned, the shotguns cleared the non-idling problems, but it still does idle completely smoothly :ummm:

One thing I haven't done yet is carb sync - but then I haven't had the carbs apart and my vacuum gauge should be arriving soon :clapping:

 

[naughtyG]

One more thing - yesterday while doing the shotgun I had a play with all four A/F screws.
I found that none had any effect at all, apart from when screwed all the way in at which point each would kill the engine. :confused2:

So I reset them as recorded when they first came off, but I'm really wondering how the hell you can tell if they're properly set or not? :ummm::ummm:

 

[maleko89]

I had a good look at PAJ 1&2 yesterday while doing the shotgun, and from memory I think they are 90 and 170.

Those are the stock jet sizes.

What about my rough idling problem? Would downsizing PAJ2 help with this?

If none of the a/f screws have an effect several things need to be checked. Throttle cables, idle speed, sync, intake boots and float level. Paj2 won't affect idle. That mainly affects off idle and small throttle openings up to 5K rpms.

 

[naughtyG]

If none of the a/f screws have an effect several things need to be checked. Throttle cables, idle speed, sync, intake boots and float level. Paj2 won't affect idle. That mainly affects off idle and small throttle openings up to 5K rpms.

Ok thanks. I think my throttle cables are ok - everything opens and closes all fine, and free play is as prescribed.
Idle speed is set to 1000rpm using the air screw.
Sync will happen soon, hopefully it'll help. I'll also check the intake boots, sounds like the carbs are gonna have to come off.

What's the deal with float level? Workshop manual mentions some special tool if I remember right - is there any workaround?

I'm still having strange idle issues though. Right after I start the bike, as soon as it's warmed up it idles pretty good. Right after a highway run or any constant riding it's also ok, but it seems the longer I let it idle the worse it gets :ummm:

For example, if I'm on a busy street, at each traffic light it gets worse, until eventually it doesn't wanna idle at all. Doing the shotgun helped, but a day after it's doing the same thing again. WTF? And all the time, running at low revs is rough, but mid to high is totally fine. I need to get to the bottom of this! :bang head:

 

[cjmeg]

Ok thanks. I think my throttle cables are ok - everything opens and closes all fine, and free play is as prescribed.
Idle speed is set to 1000rpm using the air screw.
Sync will happen soon, hopefully it'll help. I'll also check the intake boots, sounds like the carbs are gonna have to come off.

What's the deal with float level? Workshop manual mentions some special tool if I remember right - is there any workaround?

I'm still having strange idle issues though. Right after I start the bike, as soon as it's warmed up it idles pretty good. Right after a highway run or any constant riding it's also ok, but it seems the longer I let it idle the worse it gets :ummm:

For example, if I'm on a busy street, at each traffic light it gets worse, until eventually it doesn't wanna idle at all. Doing the shotgun helped, but a day after it's doing the same thing again. WTF? And all the time, running at low revs is rough, but mid to high is totally fine. I need to get to the bottom of this! :bang head:

Sounds like possibly float levels, or needle/seat.
Overfueling by too high float levels (or float needles not seating) will be fine when cold, (like when my bike was overjetted, you only needed the choke for 2-3 seconds), but would be problematic when idling, (to much fuel for too long)
A thought ..