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General Category >> Rubber Side Down! >> 36 VM Mikuni Carb. Failure to Idle
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Message started by Celeste on 04/24/23 at 19:05:01

Title: 36 VM Mikuni Carb. Failure to Idle
Post by Celeste on 04/24/23 at 19:05:01

87 Savage
Non Modified Engine
Stock Airbox
Header with DBZ killer and Baffle

Compression at 180 after 4 cranks
Ignition Coil fires and spark goes from yellow to light blue.
Engine top end was disassembled and cleaned of carbon.
Note there was excessive carbon build up.

36MM VM Mikuni Carb with Lancer specified jets

17.5, 20, 22.5, 25, 27.5, 30, 32.5, 35 pilot jets failed to establish idle

Current setting 20 pilot, 180 main, needle set 2nd from top.
On choke backfire occurs.
Off choke backfire occurs at 22.5 intermently at 3 second intervals.
Lean makes bangs. Rich mix makes thuds. No idle achieved.

What am I doing wrong or looking at?

Could be the TCI glitching? Bad jets, Bad Carb?

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 04/25/23 at 13:23:48

Lots of possibilities. I don’t think any of those pilot keys are big enough. Stick a 55 in there. Why 180 main. Stick a 155 in there. I got tired of messing with the stock carb and installed a Keihin PWK40 with only minor tweaks needed to the stock throttle cable and air intake boot. Before you go there though…

Good strong battery?

Check for vacuum leaks. Make sure the intake boot is tight and not damaged. The slightest air leak will imitate major problems.

Petcock valve functioning properly?

Those would be my first items to try.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 04/25/23 at 13:34:01

I just zoomed in on the photo and your intake set-up. I can’t exactly see it well, but no offense, it appears a bit messy. If that’s messed up in any way, it’ll never run right. Check that real close and make sure you didn’t bite a cut into it and that is is extremely secure. Good luck!

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 04/25/23 at 13:35:16

PS Lancer definitely knows his stuff. Hopefully he can chime!

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by Dave on 04/26/23 at 03:49:25

You should also be aware that this carb has an idle "air screw" for the fuel mixture.....while the original carb has a "fuel" screw.

When the idle mixture screw is on the engine side of the carb slide, it adjusts the fuel flow. Turning the screw out out increases the amount of fuel in the mixture and makes it richer.

When the idle mixture screw is on the back side of the carb slide, it adjusts air flow. Turning the screw out increases the air flow and leans the mixture.

When working with any carb - I always start with the idle mixture screw turned out 1.5 turns, and then make an initial adjustment once the bike is running and the idle speed is adjusted. The final adjustment is made once the bike is at full operating temperature.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by LANCER on 04/26/23 at 07:03:12

Did you get the VM carb new or used and from where ?
With a 20 pilot, 180 main and needle clip on the 2nd groove, it should at least start and run, assuming all else is functioning normally.
If you got the carb used then all of the tiny passageways in the carb body must be cleared if not done already. Compressed air, aerosol carb cleaner and a carb cleaning tool are used in doing this. If those passageways are not clear the carb will not function properly.

Is your header the stock unit ?
I assume the DBZ killer/baffle is a muffler of some type. Does it have a straight through section you can see through, and is its sound loud or subdued ?

Straight pipes or mufflers with no or little baffling do not work well on Savage/S40, especially on a stock engine.

From tech section review…did you check the float settings ?

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by Celeste on 04/26/23 at 08:26:56

Fellas, my timing jumped [ch128579] :-/

That’s why it’s not running. My apologies.
I’m doing a timing chain replacement.

Lancer, Amazon. Brand new. I went ahead and bought a UFO.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 04/26/23 at 08:45:34

Glad you found the culprit. That's a bummer though!

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by Celeste on 05/05/23 at 14:03:53

Rebuilt the engine. Powerful strokes, no idle still.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 05/05/23 at 14:41:01

Does it run at all? Powerful strokes?

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by Celeste on 05/05/23 at 16:06:40

No run. No idle.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by ThumperPaul on 05/06/23 at 04:44:17

I see you started a new post on this topic. DBM has outlined the technical specs of the carb and intake manifold exceptionally well! I’m really starting to wonder about the “Mikuni” you bought on Amazon…. Do you still have the old carb and intake manifold? If so, I’d clean that up again and reinstall it. If you can get it running with the stock carb, you know something is afoul with the Amazon Mikuni. That’s the quickest way I can think of to rule out other possible issues.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by LANCER on 05/06/23 at 06:43:02

VM carbs can come with needle jet, needle, pilot & main jets, etc., for 2-stroke and 4-stroke engines, in addition to knock-offs with jets (not Mikuni) either mislabeled or no markings at all.
You’ve got to know what you are buying.

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by Celeste on 05/07/23 at 11:00:47

Yep. I think I’m gonna just buy one from you at this rate…

Title: Re: 36 VM Mikuni Carb. Failure to Idle
Post by LilChop on 06/07/23 at 13:24:12

I wanted to purchase a 36mm vm carb on here, but I have no idea who to ask or purchase from. Would def. Like a whole kit as some have talked about. Also a stage 1 or 3 cam upgrade.
Thanks
LilChop