Hi Everyone,
I have a 2000 monster 750 that has been giving me grief for the last month or so. It started while on the freeway on an extremely hot and humid day here in Minneapolis (heat index was around 110 degrees FWIW) and the motor started bogging down. I had to keep the throttle open more and more to keep it running, and eventually it just fully lost power and stalled. On the side of the road it wouldn't restart. Though later that night when I picked it up it would.
I took apart the carbs, which were pretty clean inside. Replaced the gaskets anyway, cleaned everything with an ultrasonic cleaner, replaced the air filter, fuel filter and plugs, no real improvement. Checked the timing with a timing gun, seems spot on and advance is working properly. It starts pretty easily with choke, but sounds like it might be on 1 cylinder until warm. Idles ok, but bogs once you open the throttle, sometimes also backfiring into the intake runner. Once it gets into the higher RPMs it seems to run ok.
Could weak spark cause this? With the plugs out and grounded against the engine, there is some orange in the spark. Not fat and blue as I've read it should be...
Here are two videos of it running I took this afternoon:
750 w (http://www.youtube.com/watch?v=QCvKJxcDL9k#)
(engine not super warm yet, stalls / backfires visible through intake)
750 (http://www.youtube.com/watch?v=agGgvNifWc0#)
(longer, close up of airbox/carb inlets)
On the road, it will ride for a few blocks, then bog/stall when opening the throttle. I've limped it home a few times now idling in 1st gear.
Out of ideas! I'm thinking timing because of the backfiring into the intake? Maybe intake valve not seated fully upon detonation? The belts look okay. It is due for a valve adjustment -- would this be a symptom of out-of-range valves?
Thanks so much in advance for any advice or ideas!
Could be out of range valve specs. Is the 2000 FI or carbed?
JM
Quote from: the_Journeyman on August 20, 2011, 04:39:23 PM
Could be out of range valve specs. Is the 2000 FI or carbed?
It is carbureted.
My first thought was that something in the carb was clogged or amiss, because the problems were most pronounced right off idle, at the first twist of the throttle. Popping, missing, etc. But everything inside the carb seemed pretty clean.
So maybe valves out of adjustment, huh?
One thing I noticed after I shot that video, was that both cylinders seem to backfire sequentially at around the same time, when it's bogging at low RPM... Adjustment-wise, is it weird that both would need get out of spec the same amount to make that happen?
WAITING FOR A UPDATE . [popcorn]
Only two ways to rule out valves as the cause of popping, cylinder leakage test or actually measure valve clearance. I suspect you will find you have clogged pilot jets.
The first thing I would think of is bad gas or a dirty fuel filter. After checking those then I'd move down to the carbs.
Quote from: funkyzeit on August 21, 2011, 05:24:01 PM
My first thought was that something in the carb was clogged or amiss, because the problems were most pronounced right off idle, at the first twist of the throttle. Popping, missing, etc. But everything inside the carb seemed pretty clean.
Clean carbs doesn't mean that they're OK. There might be deposits inside the needles that affect (limit) the gas flow, one or both the idle mixture screws might be off, floats might be low
(http://www.ducatisuite.com/carbadjust2.jpg)
Some good info here: http://www.ducatisuite.com/jetkit.html (http://www.ducatisuite.com/jetkit.html) and here http://www.ducatisuite.com/carbsynch.html (http://www.ducatisuite.com/carbsynch.html)
Once you're sure it's not the carbs, then you can check your spark and your valve clearance (you can do it yourself, get the feeler gauges from ca-cycleworks.com). Keep posting your progress! [thumbsup]
excellent point about bad fuel/filter. Doesn't hurt to check adjustments either. Free is good [thumbsup]
Hey thanks for the responses everyone. I have replaced the fuel filter already, but I hadn't considered bad gas. I'll have to pick up a fresh gallon and see.
I have gone through the carbs, and the pilot and needle jets all seemed clean and unclogged. I ran them all through the ultrasonic washer for good measure. And everything else, really. The floats looked fine as did the little o-rings inside them. When I pulled out the carbs I noticed the idle adjustment screws were set pretty rich at 5 1/2 turns out. When I reassembled it I put them at 3.
I think I will be borrowing a compression tester and picking up some feeler gauges next and rule out the valves.
I'll post when I do. Thanks for the advice and support everyone!
What color are your spark plugs? The IMS setting may be contributing to fouled plugs. Check the needle jets for "ovality". They can wear oval from the needle and cause rough running down low in the rev range. This can happen within 5-10,000 miles. Factory Pro site and thread search has info on this.
If you have already checked this or I have missed a post, my pardon.
Quote from: koko64 on August 28, 2011, 08:33:11 AM
What color are your spark plugs? The IMS setting may be contributing to fouled plugs. Check the needle jets for "ovality". They can wear oval from the needle and cause rough running down low in the rev range. This can happen within 5-10,000 miles. Factory Pro site and thread search has info on this.
If you have already checked this or I have missed a post, my pardon.
Hey koko, thanks for weighing in. Spark plugs look pretty normal. A little grey at the tip, but no black deposits or oil or anything. I still am a little concerned about the spark not being hot enough, but I'll return to that if I check and rule out compression and valve clearances.
When I had the carbs apart, I looked for any signs of ovalling, but couldn't see any. Though I must admit I wasn't entirely sure what a badly ovalled needle jet looks like. Just now I image searched it and came up with this:
(http://www.suzuki1200bandit.com/assets/images/emuwr3.jpg)
Nothing like that going on in there that I remember, but now I am second guessing myself and wanting to look again [roll]
The backfiring into the intake is still throwing me off though -- would needle jets, or other carb problems typically cause that?
I've seen rich backfiring through the carbs and lean "spitting". If your plugs aren't fouling then it could be lean spitting with the pods, but then it would possibly be dying if you opened it up.
Orange spark isn't hot enough, you want white/blue. Original coils?
A little late to the conversation, but my 2000 M750 was doing the same thing recently. I found cracked vacuum lines to the fuel pump that were not pulliing enough fuel through the pump. Now it's riding fantastically--more power than ever!