Hi Guys,

 

I am after some advice regarding my 1979 Mk1 349. I am about 98% finished with my restoration but I have a slight issue with it. I have a new Mikuni carb fitted instead of the Amal. It starts and ticks over great. If I rev it a little bit it comes back to idle nicely. If I open the throttle fully and release it, the revs hold for 4 or 5 seconds before returning to idle. Throttle cable is not sticking and I can hear the slide in the carb returning onto the throttle stop screw.

 

I have tried the clip on the needle in different positions but it is still the same. Is this a fuelling issue or is it sounding like crank seals? The crank seals were supposed to have been replaced before I got the bike, but you never know! Am I right in thinking that when the revs hold it is running lean? Or is this normal? I have never had one before so I don't really know what it should do haha

 

I have a short video clip I could email to somebody if that would help diagnose the problem. 

 

 

I don't think that you have a problem with the seals. It sounds as you'd need a bigger slow jet.

 

Do you know the exact settings you're currently using for the Mikuni? In my experience, those carbs work very fine, but can be a little tricky to adjust.

Very nice looking bike, if you are going to ride trials with it you may find it steers better with the bars pushed further forward, take a look at how others have their bars positioned.

I don't think that you have a problem with the seals. It sounds as you'd need a bigger slow jet.

 

Do you know the exact settings you're currently using for the Mikuni? In my experience, those carbs work very fine, but can be a little tricky to adjust.

 

The carb was supposed to be jetted to suit the bike so I am not sure what is in there. I know the needle is a 5DP7, but I think I will have to strip it down to find out the rest.

 

The Mikuni is brand new.

I have just stripped the carb to see what was in there!

 

Slide  - 2.0

Main Jet  - 130

Pilot Jet  - 32.5

Needle  - 5DP7

Needle Jet  - 182 0-8

Main Air Jet  - 1.7

 

From a google search I found somebody running the same apart from he had a 35 Pilot jet.

For a Cota 330, we used a Mikuni VM 28 with these settings: 

 

Main jet: 130

Pilot jet: 40

Needle jet: 169-O0

Needle: 5F21

Slide: 2,5

Air screw, 1 and 1/2 turns.

 

 

Don't ask me why, but we found a tremendous change between 35 to 40 pilot jet ... from 3/4 to full throttle! But it's my only experience dealing with Mikunis. I can't tell you if it is a general rule.

 

PS: Sorry, I forgot to tell you that those settings are being currently used at 600 metres above the sea level.

Edited October 18, 201510 yr by kingscorpion