Day 2 - Mikuni woes?

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As your bike ran fine when you first fitted the carb, you need to work out whether or not any parts in the carb have been changed, or the settings altered in any way. If they have been altered, change them back to the initial set up that was used when the bike was running well. If nothing has changed then its not going to help messing around with the carb, when it would seem pretty clear the problem is to do with something else entirely.
 
Again like I said earlier the bike didn't have enough of run on the Mikuni before I washed it for me to establish it 'was right'. Yes it ran fine but the plugs had always been sooty on the old Amals. It broke down on the unaltered settings... I'll give it a test run with what I have altered and update.
 
If you bought the Mikuni from someone in the UK able to provide parts and technical back up, then maybe it would be a good idea to contact them for advice? Sorry just noticed you bought from "Motocarb" so probably not much hope of help, advice, or parts.
 
Well Freddy... I just know that you have been waiting for someone to tell you this.
Put the old carbies back on and get it running as good as you can... And start allover again. I know it's a pain.
Obviously the fuel lines have been on and off a dozen times now, but have you checked for water in the tank.?
Stranger things have happened...AC.
 
Motocarb have been quite helpful. I have no intention of putting the old carbs back on, it is pointless (plus it would be a long drive to try and persuade the guy who I sold them to that I wished to buy them back). Also they were knackered and sold like that. Plus if you read the posts yu would have noted it sooted the plugs before....I could go on.

The engine has not seized up solid, this is a minor problem. Please no more advice thanks.
 
Fred, Dont let that Norton pull your strings. I think everyone on here has gone that road. look how hobot deals with it.
Phil
 
Sorry to upset you Fred, It was not intentional, Sometimes it's a good thing to go back to the start and retrace no matter how much experience you've got...AC
 
Not upset AussieC, no probs. Will give it a test rife tonight on the very expensive Denso iridiums!
 
Been away weekend, just got back.

Had a ride Friday night. It doesn't start as easy as it did a week ago. Bike ran ok until it got hot then it felt weak on the mid needle/main. I pluggerd chopped it about 70mph with kill switch. New iridiums looked whitish as they only had 3 miles on them but one side is clearly very sooty on both plugs.

The one thing that also 'changed' is I topped it up with fuel from a can in the garage before that first 'breakdown' last Sunday. The fuel wasn't that old from memory, about 3 months but I may be wrong. I am going to drain off today and try new fuel. I don't think the problem is the carb as it's near enough to every setting and jet size on these posts. I know the engine is worn and I'll do a few more checks (electricals etc) and then whip the head and barrel off for a look. I could stand on the kickstarter on my old commando whereas this kicks easily. Thanks.
 
Rather than messing around with the carb, would it not be easier to do some simple basic checks such as setting the valve clearances, checking the timing, and a compression test?
 
Set timing last week with a mates gun but had to rely on tacho...

Going to recheck that. Valve spot on. Yes need compression tester but it ran pretty well before winter. Just going for a tinker..
 
Decided to stop fooling myself and the inevitable. Gonna take head/barrel off. It stinks of oil....
 
If the bikes been left standing and ran ok before it was laid up, are you 100% certain the lack of compression hasnt been caused by internal corrosion in the motor?
 
It smoked heavy on the RH pot when I bought it. It always had sooty plugs on the old amals and smelt of oil. I was just hoping to egt this season out of it before the inevitable. I want to see inside it and also have a look at the cam. It's a very good bike with all the top mods so I need to get the engine right. I have resolved it in my head so the head will be off tomorrow. Thanks.
 
If your motor is smoky, its easy to determine whether or not the problem lies with the rings or the cylinder head area. Motors that smoke more on the overrun with closed throttle probably have worn valve guides, as the depression in the manifold caused by closed throttle will tend to such oil down worn guides. On the other hand smoke under acceleration is more likely to be problems with piston rings or worn cylinders.
 
FastFred said:
It smoked heavy on the RH pot when I bought it. It always had sooty plugs on the old amals and smelt of oil. I was just hoping to egt this season out of it before the inevitable. I want to see inside it and also have a look at the cam. It's a very good bike with all the top mods so I need to get the engine right. I have resolved it in my head so the head will be off tomorrow. Thanks.
Click to expand...

You are doing the right thing. My 850 had heaps of miles up on it but was getting a bit harder to start, single VM Mikuni etc' and smoking out of the RH pot and breathing heavily. But I just could not bear to not ride it until the inevitable happened. One day it just did not want to start. All the same symptoms of yours.

Compression test showed it was pretty feeble on the RH pot and not much better on the LH. Off came the head, that looked OK and then the barrells. Well, the RH piston was burnt through in two places, eliminating both compression ring lands and both pistons had shattered rings. As I took the barrels off, they fell to bits into the crankcase! Pretty amazing how tough the old 850's are.

Anyway its now got a complete new top and bottom recon kit from RGM and looking good.

Mick
 
Now on rebuilding top end with new valves guides etc. Barrel being honed and new rings, clearances ok. Bike had no heat insulating washers and valve guides were rock hard. Inlet valves very gummed up. Mikuni should run better when back together.
 
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