Author Topic: Acceleration Hesitation Help!  (Read 854 times)

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Offline Keith

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Acceleration Hesitation Help!
« on: December 06, 2017, 10:56:19 pm »
I cannot figure this one out and am stumped, please help  >:(

The problem: https://youtu.be/GOAZVPFKHS8
Notice the hesitation after the engine revs a couple of times.  You can see my hand open the throttle and then the engine responds.  The problem is 10 times worse when the engine is under load.  It actually stutters and has trouble crusing smoothly.  At this point I am wondering if it is something in the ignitions system.


This is what I have done:

-New plugs
-replacement coils and wires (both sets, no change)
-New fuel line
-Checked airbox for leaks/holes
-Steve did my carbs about 2 years ago
-Foam in airbox inlet as Steve recommended
-New fuel line
-Tested with tank elevated above normal position and gas cap open
-Fuel petcock was rebuilt about 2 years ago, took it apart and inspected it, no leaks, works fine,
-test fuel petcock flow into gas can, seems fine
-float vents are clear

I am absolutely stumped.  I know people have had fuel starvation issues, but I have checked the entire fuel system except opening up the carbs.  Has anyone experienced anything like this?

Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #1 on: December 06, 2017, 11:02:10 pm »
tell us about the foam in the airbox. how large is the piece? where is it located? are there more than one pieces of foam? Steve

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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #2 on: December 07, 2017, 12:27:31 am »
One piece of foam, it is about 3/4" in diameter and inserted in the intake (where air enters the intake box)

Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #3 on: December 07, 2017, 12:38:37 am »
One piece of foam, it is about 3/4" in diameter and inserted in the intake (where air enters the intake box)

sounds way to small, it will take a block about 2" wide, 2" deep, and 1.5" tall.

 How many holes are in the back of the airbox for the air inlet... 1 hole, or 2 ?

Steve
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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #4 on: December 07, 2017, 01:09:39 am »
One hole, the foam takes up about 1/4" of the overall inlet size.   

I agree that the foam is not optimal for good throttle response, but the problem in the video is so bad if I am doing 60 the bike hardly accelerates...it hesitates like someone where flipping a switch turning the ignition on and off very quickly and eventually picks up some what...but is not smooth at all...not like it was a week ago.

Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #5 on: December 07, 2017, 01:23:03 am »
OK, there's your problem. the airbox should have 2 holes in the back. Someone removed the snorkle. You need to replace the snorkle, and block one side of it for the carbs to work. Here's a video of the airbox tuning, you see what the airbox inlet SHOULD look like. And yes, it matters. Steve

https://www.youtube.com/watch?v=qYpgvl2zp7w
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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #6 on: December 07, 2017, 12:36:46 pm »
Thanks again for the response, Steve.   I misunderstood your question.  The snorkel is installed, I fixed my airbox following your video and made sure it had no holes about a year ago.  I also pulled the airbox out two days ago and double checked for cracks/holes with a flashlight in a dark room. 

Let me add this to the timeline.  One month ago this problem did not exist and the bike ran fine from 24k when I first bought it until 63k that it had last month.  It slowly crept up and after the tuneup last weekend it got to the point that the bike is unrideable.   The only thing I touched was the valves, the crank nut, the spark plugs, wires/coils and air filter.

Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #7 on: December 07, 2017, 01:01:58 pm »
block one full side of the airbox with foam. repeat your test. film it if you want to. unless you have a fuel blockage limiting fuel flow, the foam block is going to fix your problem. steve

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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #8 on: December 07, 2017, 03:11:10 pm »
Thanks again Steve, that's what I was thinking.  I will grab some more foam on the way home and plug the airbox up and start the process over of removing foam until it is just right.

Offline connie_rider

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Re: Acceleration Hesitation Help!
« Reply #9 on: December 07, 2017, 03:52:20 pm »
Oh oh,, you sed "the crank nut"..
Did you apply e'nuff force to the "crank nut" to shear the pin in the crank?
  ie; Were the plugs out when you turned the engine?

Ride safe, Ted
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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #10 on: December 07, 2017, 05:02:17 pm »
Plugs were not out when I turned the engine.  I did the spark plugs then the valve adjust.   I was very gentle with the cranknut, but this is something else worth taking a look at when  I get home tonight.

Offline Bud

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Re: Acceleration Hesitation Help!
« Reply #11 on: December 07, 2017, 05:43:58 pm »
Plugs were not out when I turned the engine.  I did the spark plugs then the valve adjust.   I was very gentle with the cranknut, but this is something else worth taking a look at when  I get home tonight.
It's best to leave the cranknut alone.  When doing a valve adjust, it's best to bump the starter button to roll the engine over.  An alternative is to put it in gear and turn the rear wheel.  Spark plugs are out in either option.  I'm with Ted on this one.

Offline connie_rider

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Re: Acceleration Hesitation Help!
« Reply #12 on: December 07, 2017, 09:45:46 pm »
I kinda think you didn't hurt the nut.
Went back and listened to the video.

First look at what Steve sed.
Then, back to basics, check spark plug wires/caps, carb boots etc.


Ride safe, Ted
« Last Edit: December 08, 2017, 03:36:10 pm by connie_rider »
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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #13 on: December 08, 2017, 02:15:01 am »
Tonight I tried more foam.  I blocked off one side of the airbox, at the end of the video I removed the foam completely.  I did check the crank "nut" and everything is ok.

I also pulled the tops of the carbs and checked the diaphragms, which are all ok.  The carbs look spotless inside and the slides move without any binding.

https://youtu.be/v6a0Og8g9uQ

Offline Mettler1

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Re: Acceleration Hesitation Help!
« Reply #14 on: December 08, 2017, 03:57:45 am »
   My only guess is that it's fuel starvation. I have a feeling the carb gas passages are plugged or not enough fuel in the float bowls. Do you use fuel with ethanol. Ethanol can plug carb passages if it sits for a long period.
  Also are the carb boots to the engine TIGHT!!

   Again it's not enough fuel OR TOO MUCH air!  Just rambling trying to get ideas flowing>   ::)

   If you find the problem let us know. I'M DYING TO FIND OUT!!!!  :-[ :-[
« Last Edit: December 08, 2017, 04:03:17 am by Mettler1 »
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Offline EZ

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Re: Acceleration Hesitation Help!
« Reply #15 on: December 08, 2017, 09:53:38 am »
Kind of acts like there is water in the fuel.
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Offline Bob_C_CT

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Re: Acceleration Hesitation Help!
« Reply #16 on: December 08, 2017, 11:00:14 am »
Did you test fuel flow of petcock while in prime? Get the bike running then switch to prime and see if that makes a difference. Make sure not to leave it prime after test.
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Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #17 on: December 08, 2017, 11:17:40 am »
the fact that it seems to have a reliable idle should eliminate things like poorly adjusted valves and ignition issues. It appears to me that either it's getting to much air, or there's very low fuel in the bowls. enough for idle but not enough to run rpms. so I'd check fuel flow, and also is the airbox door on and sealed up? Air filter properly seated? Is this engine warmed up fully when you're doing these tests, and how does it act if you do these tests with the enrichener pulled on? Steve
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Offline Bud

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Re: Acceleration Hesitation Help!
« Reply #18 on: December 08, 2017, 03:00:43 pm »
I watched that last video a few times.  I noticed that at the very beginning of the vid, he had the enrichener on enough so that the idle should have been considerably higher than what it was.  When he turned off the enrichener there was no difference in rpms.  What does that tell us?

Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #19 on: December 08, 2017, 05:55:05 pm »
time to answer some questions:

-I do use fuel with ethanol, but this bike does not sit.  I ride it year round and 80 miles a day 4 days a week.  It is my daily driver. The longest it has sit is for a week while on vacation. 
-doubtful there is water in the fuel.  This tank is 4 days old and was always sealed.  Plus I added more clean fuel to it and drained off the lower portion
-I have been running the bike on prime and switching to ON and reserve.  I also disassembled the fuel petcock ( which was rebuilt 2 years ago) and checked for flow.
-air box is sealed, removed and checked for cracks/holes.  I also did the airbox fix a year ago and added silicone to the door so it has a proper seal.
-If i do these tests with the enricher on it acts the same, but much more rich...can smell gas in the exhaust big time
-Engine is warm when doing the tests (though it acts like it does when it is cold.
-My enricher has always done very little from the 12:00 to off.  When i pull it further foward past 12:00 is when the cable starts to pull.  I have a new enricher cable and have verified the throw on the carbs....it just so happens that my throw is not linear.   I do know the enricher is working because with it on you can smell the extra gas in the fuel and the bike doesn't run very well when warmed up.

I put the bike back together this morning, made sure all my fuel vacuum  connections were good and with brand new hose...no kinks.  I filled one side of the air snorkel with foam minus about a finger's gap.   Also pulled #4 plug and it still looks new.  Last night I disconnected each plug to verify a drop in idle for each plug pulled and there is one.

It feels like the bike is running fine until there is a demand for gas and the floats empty.  The first couple of revs are always perfect, then it hesitates.
Problem still persists....

Offline connie_rider

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Re: Acceleration Hesitation Help!
« Reply #20 on: December 08, 2017, 08:00:53 pm »
Keith.
Some questions..
Do you have 1 vacuum line (from #2 cyl) hooked to the petcock, or do you have 2 paired together and then hooked to it?
Do you have a rich smell when idling?
Did you have to turn the idle speed screw extra far in to make it idle?
Did you go back and check the coil ground and wiring?

Ride safe, Ted
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Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #21 on: December 08, 2017, 10:52:36 pm »
I have one vacuum line from #2 to the petcock. All other vacuum lines are capped with new rubber caps.
I do not have to turn the idle screw in excessively get it to idle at 1krpm
the coils have been replaced with spares, all grounds checked. 
I have done Steve's free power mod to the igniter and it has a ground directly to battery.
The bike does smell rich at idle with the enricher off.

Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #22 on: December 09, 2017, 12:10:54 am »
I think it may be fixed.  Rode it 20 miles on the highway and so far running better than ever.  I will update later with what I did.

Offline Keith

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Re: Acceleration Hesitation Help!
« Reply #23 on: December 09, 2017, 02:53:08 am »
Rode about 25 miles tonight mixed highway/city and I had no hesitation.  The only two things I think that could have fixed it are:

1. my air filter foam gasket is stretched and was leaking air.  I need a new one for my K&N, but I was able to squish it so that it no longer leaks.
2.  I got the foam in the airbox snorkel closer to right.  The bike still smells rich at idle and I fear my gas mileage may be below normal, but I can always adjust that later.

Offline Steve in Sunny Fla

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Re: Acceleration Hesitation Help!
« Reply #24 on: December 09, 2017, 11:08:30 am »
The foam size doesn't have anything to do with idle, so don't mess with the foam to straighten out the idle. assuming float levels haven't crept to high, you can adjust the idle fueling with the bleed screws for the low rpm,  and adjust the foam for higher rpm.  Aren't you glad you didn't send the carbs back now? Steve
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