cliff montesa Posted October 18, 2015 Report Share Posted October 18, 2015 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. Quote Link to comment Share on other sites More sharing options...
kingscorpion Posted October 18, 2015 Report Share Posted October 18, 2015 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. Quote Link to comment Share on other sites More sharing options...
collyolly Posted October 18, 2015 Report Share Posted October 18, 2015 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. Quote Link to comment Share on other sites More sharing options...
cliff montesa Posted October 18, 2015 Author Report Share Posted October 18, 2015 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. Quote Link to comment Share on other sites More sharing options...
cliff montesa Posted October 18, 2015 Author Report Share Posted October 18, 2015 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. Quote Link to comment Share on other sites More sharing options...
kingscorpion Posted October 18, 2015 Report Share Posted October 18, 2015 (edited) 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, 2015 by kingscorpion Quote Link to comment Share on other sites More sharing options...
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