5th gear/decel issues

Vtunimog · 07-04-2019, 11:31 AM

I took a long ride yesterday and the hawk performed just fine but noticed on some steep climbs around 40 mph the engine raced a couple times in 5th, I noticed if I downshifted then shifted back up to 5th it was ok.

At the end of my ride (about 120 miles or so) it was cooler out and when I would run at about 1/8th throttle in 3-5th gear I would get a perceptible skip. I run a 115 main and stock pilot. Any ideas ? I think the needle is in the 4th position but honestly don’t recall. I changed out the carb for a VM26 and changed out the main for 115. I don’t get any popping on decel but if I hit the throttle too quickly I get a bit of a jerk.

I do have the aftermarket exhaust, stock air filter, I am running Amsoil dirt bike 50w - I did notice these symptoms started right after changing my oil, I assume unrelated.

I have about 1700 miles on the bike.

Thanks in the advance for any advice

Sochin · 07-04-2019, 12:39 PM

Skip......like in the engine racing in rpms while you hold a steady throttle? Make sure your clutch cable isn't too tight. Adjust it a little loser so the clutch doesn't engage when oil gets hot. I've got about 2700 miles on my 2017 model......and mine does this after long highway runs sometimes.

Weldangrind · 07-04-2019, 12:55 PM

You say you're running the stock slow jet; what size is it? Have you adjusted the valves recently?

Megadan · 07-04-2019, 01:10 PM

Quote:

Originally Posted by Vtunimog

At the end of my ride (about 120 miles or so) it was cooler out and when I would run at about 1/8th throttle in 3-5th gear I would get a perceptible skip. I run a 115 main and stock pilot. Any ideas ? I think the needle is in the 4th position but honestly don’t recall. I changed out the carb for a VM26 and changed out the main for 115. I don’t get any popping on decel but if I hit the throttle too quickly I get a bit of a jerk.

Your own clue is the 1/8th throttle part. That instantly rules out the main jet (3/4 to wide open) and with the needle jet in the 4th notch, the needle setting as well.

The other dead giveaway to this issue is the "stock pilot", which just like the original pz30 carb, is too small. Usually the VM26 clone carbs come with a 20 pilot jet, and ideally you will want a 25 or 27.5. One of the ways to judge pilot jet size is by holding steady light throttle (up to 1/8th turn) in a higher gear. That "skip" is hesitation brought on by running lean on the pilot jet, and it can happen even if your idle mixture seems good. Up the pilot jet size.

As far as the engine "racing" in 5th gear, some more details would be helpful. Are we talking like the RPMs just increased? If so, it sounds to me like your clutch may be adjusted a little too tightly and is slipping, which always tends to show itself in a high gear under high load. If you adjust it back out a bit and it still does so then the clutch is either not fully engaging due to a mechanical reason or the plates are worn out, which is unlikely given the miles but still possible.

Vtunimog · 07-04-2019, 02:22 PM

I didn’t think of the clutch cable. I will back it off slightly and see if that helps. The odd part is I have experienced a slipping clutch (I learned to ride on an old Hodaka someone gave my dad, the poor clutch plates would slip like crazy and the engine would scream). This case the engine revved pretty high then re-engaged the gear pretty hard.

MegaDan I meant to say I recently picked up a Keihin PK30 I am still running the vm26.

I will look into a 25/27.5 jet.

Vtunimog · 07-10-2019, 06:18 PM

I feel like Will Farrell in Land of the Lost - "that is immediately worse" he dumps Trex pee all over his face. My friends at Dennis Kirk sent me a 25 and 27.5 slow/idle jet. I noticed there was a slight taper above the threads which made tightening the 27.5 a bit strange it got tight then as I cranked it down it finally seated. Anyways took it out climbed a hill and got sputtering under load, if I was at 3/4 and above ok, but if I was under heavy load ( I have a steep hill that is about 1 mile I climb on dirt) I would get a perceptible skip or sputter. one the flats coming off full or 3/4 throttle if I back off quickly at about 1/4 I get sputtering, slowly let off. should I go down to the 25 idle jet ?

I checked again on the needle it is below the 4th notch ? at what looks like it's lowest position.

Ok looked up the setup for a VM26, looks like there are 5 notches and mine is definitely in the lowest. If I understand correctly the screw to the right of the carb is the Idle Speed scew which right now seems to no be making much difference ??

the screw below the bowl is the mixture screw ? how the hell do you adjust that (I have a right angle sloted screw driver but it definitely wont fit) do you take the carb off - adjust and put it back on ?

Second go at it - idle 4K no idea why. Wound it up to 7000 and it was like what ChipToothy described in his post the bucking/stutter was crazy. got the bike home turned it off and a pop and blue flame out the muffler. it has to be mixture. I cannot for the life of me figure out who to adjust the screw below the bowl. I am about 3/4 of the way to saying screw it and putting on the old stock cheapo carb or the new PK30P I have. Or maybe just have a drink of 4 and calling it a day.

really perplexed.

Vtunimog · 07-11-2019, 05:20 PM

I didn't solve the issue but changed out VM for a PZ30 , everything made the condition worse. I finally took out the 27.5 idle jet and found it was in this condition - see attached -

the Dennis Kirk jet has a very gentle stop which means if you aren't careful you can keep cranking it until it feels tight. removed that put the 25 in, better but once hot the WOT at 7000-7500 stumble was enough to make me crazy. Ran fine all year, last winter some mice made a nice nest in my airbox so I stored it inside and this is what I get for a nice constant 67F humidity controlled basement.

so I got frustrated pulled the carb off and put on the Kiehen and so far so good. throttle takes a pretty heft pull with the split cable I may upgrade the throttle kit Megadan and others have.

I read through the pumper carb threads and I think it was the right decision. it was fairly easy to hook up great job to everyone who mapped out the process previously.

07-04-2019, 11:31 AM	#1
Vtunimog Join Date: Sep 2017 Location: Vermont - USA Posts: 73	5th gear/decel issues I took a long ride yesterday and the hawk performed just fine but noticed on some steep climbs around 40 mph the engine raced a couple times in 5th, I noticed if I downshifted then shifted back up to 5th it was ok. At the end of my ride (about 120 miles or so) it was cooler out and when I would run at about 1/8th throttle in 3-5th gear I would get a perceptible skip. I run a 115 main and stock pilot. Any ideas ? I think the needle is in the 4th position but honestly don’t recall. I changed out the carb for a VM26 and changed out the main for 115. I don’t get any popping on decel but if I hit the throttle too quickly I get a bit of a jerk. I do have the aftermarket exhaust, stock air filter, I am running Amsoil dirt bike 50w - I did notice these symptoms started right after changing my oil, I assume unrelated. I have about 1700 miles on the bike. Thanks in the advance for any advice
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07-04-2019, 12:39 PM	#2
Sochin Join Date: Jul 2017 Location: Montucky Posts: 209	Skip......like in the engine racing in rpms while you hold a steady throttle? Make sure your clutch cable isn't too tight. Adjust it a little loser so the clutch doesn't engage when oil gets hot. I've got about 2700 miles on my 2017 model......and mine does this after long highway runs sometimes. __________________ 1983 Honda Xl600R 2016 Ducati Multistrada 1200S DVT
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07-04-2019, 12:55 PM	#3
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	You say you're running the stock slow jet; what size is it? Have you adjusted the valves recently? __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
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07-10-2019, 06:18 PM	#6
Vtunimog Join Date: Sep 2017 Location: Vermont - USA Posts: 73	Immediately Got Worse I feel like Will Farrell in Land of the Lost - "that is immediately worse" he dumps Trex pee all over his face. My friends at Dennis Kirk sent me a 25 and 27.5 slow/idle jet. I noticed there was a slight taper above the threads which made tightening the 27.5 a bit strange it got tight then as I cranked it down it finally seated. Anyways took it out climbed a hill and got sputtering under load, if I was at 3/4 and above ok, but if I was under heavy load ( I have a steep hill that is about 1 mile I climb on dirt) I would get a perceptible skip or sputter. one the flats coming off full or 3/4 throttle if I back off quickly at about 1/4 I get sputtering, slowly let off. should I go down to the 25 idle jet ? I checked again on the needle it is below the 4th notch ? at what looks like it's lowest position. Ok looked up the setup for a VM26, looks like there are 5 notches and mine is definitely in the lowest. If I understand correctly the screw to the right of the carb is the Idle Speed scew which right now seems to no be making much difference ?? the screw below the bowl is the mixture screw ? how the hell do you adjust that (I have a right angle sloted screw driver but it definitely wont fit) do you take the carb off - adjust and put it back on ? Second go at it - idle 4K no idea why. Wound it up to 7000 and it was like what ChipToothy described in his post the bucking/stutter was crazy. got the bike home turned it off and a pop and blue flame out the muffler. it has to be mixture. I cannot for the life of me figure out who to adjust the screw below the bowl. I am about 3/4 of the way to saying screw it and putting on the old stock cheapo carb or the new PK30P I have. Or maybe just have a drink of 4 and calling it a day. really perplexed. Last edited by Vtunimog; 07-10-2019 at 07:56 PM. Reason: Because I am a fool mostly
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07-04-2019, 02:22 PM	#5
Vtunimog Join Date: Sep 2017 Location: Vermont - USA Posts: 73	I didn’t think of the clutch cable. I will back it off slightly and see if that helps. The odd part is I have experienced a slipping clutch (I learned to ride on an old Hodaka someone gave my dad, the poor clutch plates would slip like crazy and the engine would scream). This case the engine revved pretty high then re-engaged the gear pretty hard. MegaDan I meant to say I recently picked up a Keihin PK30 I am still running the vm26. I will look into a 25/27.5 jet.
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