1982 XJ550 VM34 Turning advice

Hello everyone,

First, let me thank you for your patience. This is my first motorcycle and my first time tuning carbs. I bought the Murray's VM34s and they haven't ran well at all. I live in Denver and after checking the spark plugs, the carbs are running rich. Some of the guys at work think I may need to go down a few sizes on my jets, but if I'm being honest I don't know where to start. This bike has been problem after problem but I'm committed to getting it running again. Any advice or links would be extremely helpful.

Thank you in advance!

 

Hello there,
this won't help much but what was wrong with the original Mikuni carbs?
Are you running without the original air filter and using pod filters?
Also, the original Mikunis were 28mm and not 34.

 

I bought the bike without carbs. It was a project from the start but I figured two carbs would be easier to tune than four. The original air box has been removed and it came with two K&N pods

 

So it's a twin cylinder bike and not 4?

 

4 cylinders, two carbs, custom manifold. I bought the kit picture.

 

Right ok. I don't know these Murrays aftermarket carbs but have heard they supply good alternatives.
Is there a mixture adjusting screw somewhere on each carb? The mixture screws might just need a slight adjustment.

 

I have them next to bottomed out. It won't start otherwise. My work friends want me to get smaller jets for it and see if that corrects it but I have no where people are getting the jets because all I'm seeing are eBay kits and Chinese knock offs of mikuni. I want to do it right (or at least as right as I can). Thanks for your help btw. I really do appreciate it.

 

No problem mate.
Another question for you, what petrol are you using. Here in the UK most people that ride bikes are using the E5 petrol and not the E10. Just a thought.

 

I only use ethanol free if I can help it. In a pinch I used e10 but it was removed when I got my new tank. It came with a tank for a xj650/750 I think.

 

Can't say for sure since I am not familiar with your full setup, but those don't look like CV carbs. My general experience is that non-CV carbs tend to run rich here in Colorado due to our altitude/thinner air. Most of my bikes I've had to go down at least a size on the mains to get them running clean. That won't affect the low speed though. You could also be rich on the pilot. When you purchased the kit, did you tell them what altitude you would be running at? They may have recommendations for proper jetting.

 

I didn't really think about that but I kind of assumed someone would look at the shipping information to figure it out. That's on me lol. I'll figure out what jets are on the carbs today and message them.

 

I would suggest that you contact Murray directly, I have spoken with him a few times and he seems to be a very knowledgable and helpful person:

Murray’s Carbs
PO Box 1824
Welcome, NC 27374
1-336-491-5336
https://murrayscarbs.com
murray@murrayscarbs.com

https://murrayscarbs.com/idle-screw-adjustment

Don't forget that operating a bike with flat-slide carbs (racing carbs, really) is a lot different than the CV carbs that most street bikes use. CV carbs basically make "flooding " the engine (too much throttle too soon) impossible as the vacuum-regulation of the fuel flow is basically "automatic" and requires little to no user regulation. With flat-slide carbs, cranking the throttle open gets lots of fuel flowing immediately.....basically you have to feather the throttle a bit (especially off idle) and let the engine "catch up" to the throttle position (which you control). YOU have to keep up with the engine rather than letting the carbs (CV's) do the heavy lifting. Not having the "feel" of how to do that can lead to overly rich conditions. A bit of "throttle patience" and experience will overcome that problem.

 

Thank you for that information. Hopefully the necessity of learning how to control the throttle will make me a better rider lol