New Mikuni issues on fresh motor MKIII
- Thread starter Coco
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rx7171 said:
I'm also thinking not a valve issue.
I talked to CNW who rebuilt my motor and they say not to worry too much about the one black plug since I have not had a chance to bed the rings yet so I'm probably still getting a bit of blow by on the right side. He also mentioned needle poistion would not make any difference but at this point I'm willing to try anything.
What I can't figure out is why the bike seemed to run great and never did what it is dong until 10 minutes into the 50 mile ride I needed to do to bed the rings.
The bike also revs well when static. I can get it up to 3000 rpm to time it without any symptoms, just when I'm under load is this happening.
I went over all the ignition connections and the grounds on the bike. I then decided to pull the Trispark out and see what was going on and the damn magnet was not very tight on the cam taper and I could see evidence of light wear marks. The bolt was lightly snug at best.
How much torque should one use on that bolt?
That has to be it. I'll get a buddy over here later and retime it and then try again with some fresh plugs. Cross your fingers for me boys.
How much torque should one use on that bolt?
That has to be it. I'll get a buddy over here later and retime it and then try again with some fresh plugs. Cross your fingers for me boys.
GRM 450 said:
I tried that. I opened the tank cap while riding and same thing. Whentaps are opened, I can see fuel run into the fuel lines quickly ect. I'm only doing around the block rides so there would be more than enough fuel in the floatbowl to avoid starvation issues on that short 2 minute ride.
I'm about to grab the hammer.
Coco said:
http://www.mikuni.com/pdf/vmmanual.pdf
Page 12 has the float height. It's better to use throttle opening instead of RPM's when you're thinking about jetting for anything but the main. It helps to put some masking tape on the grip with marks so you know where you're at. Is there any throttle opening that the engine runs ok at? When the engine is warmed up, do you get any response to adjusting the airscrew? Often you can get out of or into jetting problems by slowly opening the throttle, meaning particular circuits phase out and others come into play. If one of them is way off it becomes apparent. I'm thinking rich by what you describe. I'm at sea level but ride up in the mountains a lot. VM34 with 25 pilot, 3.0 slide. I chased it down from 40 and 2.5, but the temps around here are probably nothing like what you're seeing right now.
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I just had this same issue on my bike exact same symptoms with an amal and single carb manifold. Turned out to be an air leak and/or defective manifld or a combination. when I put on a proven manifold and carb the bike ran as it should, that is until a valve stuck open.
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I have a non-matching set of mikuni carbs in my bike. (Air ports are different, chrome slide vs brass or something) Got another carb to match, installed it, swapped the jets over, and had the same symtoms as coco. Tried to get it to run, couldn't figure it out. Put the old carb back in with the same jets, Ran like a charm......
Coco said:
As I said, the stems seem sooo buttery in the guides at assembly and ran fine at first. Looking back, the first incination of trouble was it took a few more kicks then usual to start. Eventually is got just tight enough and took an ever so slight tonk from the piston. Thank goodness it was idling in the driveway.
Not knowing what the hell was happening at the time, the compression test told the tale.
Check and compare your compression. If you do not have a screw in tester, get one for around 25 bucks. It seems that i use mine as often as the timing light.
Whether it a guide or something else, check it anyway. I does not matter how reputable a company is, shit happens, particularly right after rebuilds.
And by the way, it was the exhaust valves that were/got tight.
pvisseriii said:
After timing and tightenig the magnet the test ride that followed showed the plugs are the same colour. I'm still getting a bit of blow by on the right cylinder due to the rings not being bedded yet.
Choke and idle adjuster ect all make the carb run differntly when adjusted or turned so the circuits must all be working.
At this point it could very well be a faulty Trispark unit. I'm going to try a diffeent carb from a friend and see what that does. Then I'll try another Trispark unit.
britbike220 said:
The manifold I have is a brand new MAP unit. I actually levelled both mating surfaces before installing since the casting was a bit rough. The bike ran great up through 3rd gear until 10 minutes into a long ride so if it was a manifold problem, that would have been noticed on the small test rides i did leading uo to long ride, where the symptoms started 10 minutes in.
I have not looked at the flange to spigot adapter so maybe I'll peek at that today. It is new as well but maybe has a crack?? Wouldn't an air leak cause idle to rise though, even at idle?
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Just throwing it out there. I thought the map unit was inferior and more expensive compared to the RGM unit. I have ordered another RGM.
Do you have stock coil or a Dyna coil type, If dyna, You do know that these EI systems spark both sides at the same time so simply swapping a plug wire from the coil output will diagnose the unit. If the Tri or any other unit of this type is bad, neither cyilinder will fire.Coco said:
What did that compression test show?
Coco,
This thread is getting epic. Back to the beginning - this is a newly built motor? Does the bike turn sour around 4,000RPM, i.e. just won't rev out? and seems to stumble? Reason is that if the cam timing was out by 1 link pin, these symptoms will occur. I have witnessed this and believe me, carbs, exhausts, ignitions system all pulled and replaced and finally it was incorrect cam timing.
Hope that helps.
Mick
This thread is getting epic. Back to the beginning - this is a newly built motor? Does the bike turn sour around 4,000RPM, i.e. just won't rev out? and seems to stumble? Reason is that if the cam timing was out by 1 link pin, these symptoms will occur. I have witnessed this and believe me, carbs, exhausts, ignitions system all pulled and replaced and finally it was incorrect cam timing.
Hope that helps.
Mick
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