HarleyTechTalk

A friend just got an Evo Wide Glide with a pretty serious stalling problem.  Right off idle it has a stumble from when the throttle is first opened until engine speed picks up.  The accelerator pump is fine.  This stumble is bad enough to be dangerous if traffic is coming.  It works fine at idle and with plenty of throttle, it is just this off idle to part throttle stumble that is causing trouble.  He has driven with the choke in and out and with the idle mixture screw in and out, and nothing helps.

He has drag pipes which could be causing this.  They have the stock HD pipe diameter coming out of the port, but quickly go up to about a 2 1/4" diameter.  There is no sign of a vacuum leak, but we are going to check that one more time later this evening.

The carb had sat for a while, so I soaked it in carb cleaner, blew it  out with compressed air, and reassembled it.  It has a Dynojet kit which I left in.  The main jet size is 170.  It had a 42 idle jet which I changed to 45, but had no affect at all.  The idle mixture screw adjustment does not help.  The slide had the hole drilled out to about 1/8", so he changed the carb to one closer to stock with no change.

He picked up a used CV in good shape (he cleaned it and it looked good inside) and put it on in place of the other CV.  Again, no change.  He changed the ignition and checked as many grounds as he could find.  Same old same old.

My advice was to put on sensible pipes, but I have several friends with drag pipes who do not have this problem.  Any pointers to put us in the right direction?  Maybe wad up some steel wool and cram it into the pipes just to see if it changes?

Make sure the needle jet is not upside down. The open end goes up into the venturi.


JB

Has it done this since he first bought it or did it start some time after? Did you do a compression check? What do the plugs look like? What year bike? Possibly bad compliance fittings or intake seals. Did you make sure there are no open vacume ports on the rear of the carb? Also the idle mixture screw o-rings don't last forever. Just a bunch of easy things to check. I'm not sure where you're at but down here at sea level even a 45/170 combo might  be a bit lean with intake and exhaust mods and with those pipes.....

Quote from: JBarrettB on September 07, 2010, 10:43:16 AM
Make sure the needle jet is not upside down. The open end goes up into the venturi.


JB

Exactly the problem I had in 1996 when I tore into my first CV.  Had the same results you are describing

Some good suggestions, thanks.

The bike is a 1995 Wide Glide and we didn't do a compression check.  It runs pretty strong when the throttle is pinned, so the engine seems strong enough.  I live in Florida at an elevation of about 13 feet.

I've mixed up needle jets myself and always felt pretty dumb when I found I had put them in backwards.  This is a strange CV.   The needle jet would only go in one way - first one like that I've seen.  I thought I had it crooked so I tried it both ways from within the venturi toward the bowl just to be sure.  Same thing, the inside was a slightly larger diameter than the bowl end.  So it is correct.  The carb was so bad that the accelerator pump was stopped up and the diaphragm was cracked.  I had a spare bowl to change it to, but that had nothing to do with the problem.  I'm just saying how bad this thing was.

The bike was bought used and the man who sold it said it was running fine when he parked it, but it had been sitting for several months or longer.

I blew out the transfer ports in the carb and they were slightly plugged, but the replacement carb was clean and not plugged and it does the same thing.  We checked the intake seals and vacuum plugs and they all looked good.  In the next few days we'll look at everything closer to be certain of all this.  At this point, we are not sure it was running all that good, or if he just said so to make the sale.

The carb has a Dyno Jet kit in it, and I'm not sure it directly corresponds with Harley jet numbers.  That is, I don't know if a DJ 170 main jet flows the same as a HD or Yost 170.  There were only two bleed holes in the DJ emulsion tube, so I'm thinking about changing back to HD.  I doubt this is the problem, though, but it might make it a little better.

The scoot used to have baffles in the pipes, but there's nothing but hollow cans now.  Even the screws that held the baffles in were gone.  Going from 1 3/4 to 2 1/4 on the pipe diameter with no baffles with all, plus the carb problems makes this a challenge to fix.

I had a similar problem on my FXR and it turned out to be the tach wire.  That's not the problem with this one.

Thanks for the help and anything else you might think of.  I think this will be one of those things that takes a couple weeks to find and 15 minutes to fix.

170 main is way too small in my experience. I run 185 on my 96 dyna. 
Your tune may vary, but not that much.

Those pipes aren't helping either.  2-1/4" is WAY too big for an 80ish inch motor.
You greatly reduce the velocity and scavenging effect of the exhaust gases.
Open drag pipes will lean out a motor significantly, requiring a richer jet.

First, I agree that 170 is really too small (my 1200 sportster came with a 175 main).  You say that the bike idles fine (kinda rules out vacuum leaks).  That you can throttle the bike while it's sitting and that's fine (right?).  The bike seems to really fall on it's face at one particular throttle setting?  I would suggest this would indicate that you have an overly small main jet and the needle that you are running is incorrect or needs to be adjusted (if adjustable).  However, it's going to be really difficult to fine tune the carb with those hollowed out pipes.  Can you convince the owner to get something else?  I'm afraid that with these pipes, the bike may not be tuneable and even if you make it better, it just wont ever be "good."

When I first bought my FXR it did exactly the same thing.  It too had a dynojet kit installed. Turned out the dude who installed the dynojet used the wrong sized drill to drill out the hole in the slide (too big). Bought a new slide and diaphram, drilled a smaller whole and all was good. (the guy who sold me my bike said it ran fine too - I think the truth is he never figured out what was wrong with it either so he sold it.) Could it be that both your carbs have the same problem?

A dirty air filter and a dirty gas line filter will cause a blip in the low end of throttle! The 45 low seems right and even if the 170 is small, you should still be able to roll in the low end until the main is needed!

Jetting is an issue that seems to come up alot. There are lots of folks that drill the slide and lots that don't agree with this process. I personally don't .    Here is what I have posted on the jetting subject:
Here is what I have posted before on this subject.
To start here is some info that might help: It is my opinion that all Harley's are jetted lean from the factory to help meet EPA regulations. This is why they will only run 80MPH and are so cold natured. When I bought my evo in 96 it was so cold natured that if I stopped for 30 minutes,I had to choke it to start even had I been riding for hours. I fixed this buy going to the Sportster needle and a 45 slow jet Now several years later and after Stage 1 and Stage 2 upgrades I have a 80 inch EVO with EV27 cam, Hypercharger w/k&n filter, Hooker 2into 2 upswept slash cuts, CV carb with Thunderslide kit. I went with a 185 main and a 46 slow.  Bike runs great and still gets about 45 mpg.
I would start by obtaining a supply of mainjets "175/180/ 185/ 190" and slowjets "45/46/48"going back to the instructions (I here Thunderjet needles and tube work better with Thunderjet jets)and setting the carb up as suggested. My start would be a 45 slow with a 180 main and set the needle back to the position the instructions said.  Pop out the aluminum cap that covers the adjustment screw and get the Idle right.Then the easy way to get it close on the top side is to warm the bike up and get out on the hyway (where there are not any law enforcement)  and run up to about 4500/5000 rpm in fourth gear and hold it there for a minute then back off the throttle about an 1/8 of a turn. If the rpms go up you are still lean, if they go down you are probably rich. If there is no difference it is about right. if you have no tach you can tell buy the seat of your britches if it pulls harder or not. Check out  http://nightrider.com/ for good info on tuning your carb
Good Luck 

Buy a cheap set of baffles or mak some out of washers and bolts and put in the pipes. see if that helps     

Quote from: Bullwinkle on September 07, 2010, 09:13:16 AM
A friend just got an Evo Wide Glide with a pretty serious stalling problem.    It has a Dynojet kit which I left in. The main jet size is 170.  It had a 42 idle jet which I changed to 45, but had no affect at all.  The idle mixture screw adjustment does not help.  The slide had the hole drilled out to about 1/8", so he changed the carb to one closer to stock with no change.

He picked up a used CV in good shape (he cleaned it and it looked good inside) and put it on in place of the other CV.  Again, no change. 

The CV jets sizes are not the same as the dyno jets sizes, not sure what emulsion tube you are running now stock or dyno jet one?

See attached...

[attachment removed after 60 days by system]

what part of the igntion was replaced ? I recently replaced a coil on a bike that had a horible off idle stumble ,kicked my ass for while fussing with the carb.  Oh yeah this bike would start kinda funky at times also .

A quick follow up.  Not a lot of time here the past couple of weeks.

He got rid of the 2 1/4" pipes in favor of 1.75, but still drag pipes.  Money is an issue and they were cheap.  I have no idea whose aftermarket carb kit is being used, but the emulsion tube only has two holes which looks like a Dynojet kit.  The needle doesn't look like any DJ needle I've seen.  It is brass, adjustable, but very little taper.  It may be old, or may be a cheap clone.

The whole ignition system was changed to an Ultima cone module and single fire coil.

I gave him a stock HD emulsion tube, needle, and 185 jet, not neither of us has had time to put this thing together.  He bought a used CV with an undrilled slide, so between all this the carb should be close enough to work safely.  That is, to not stall in the middle of pulling out onto the street.

Maybe by the weekend to early next week it will be running and I'll report back here what it took.