belldane Posted August 8, 2009 Report Share Posted August 8, 2009 Hope someone out there can give me some clues about my 348. The bike has always been hard to start from cold. It is running the standard Amal monoblock carb which was recently resleeved etc etc. Once the bike warms up it is fine although the amount of smoke it produces is embarrasing. (exhaust and muffler were hit with an oxy to burn all rubbish out) Fuel consumption is terrible. I went for a short ride today around the property and ran out of fuel coming back home. I put in just over 2 litres of fuel before heading off and would not have done more than 5 kilometres riding. There are no fuel leaks anywhere. It still has plenty of power but the above problems are driving me to drink (more). I really think that the carby is not working like it should but for the life of me I can't put my finger on the problem. All jetting is standard, although I have tried different sizes all to no avail. I changed the carby to an old Mikuni I had lying around and after a few kicks it started with not as much smoke but when I took it for a ride everything else was pear shaped. Any ideas what the problem could be please? I really am running out of ideas. Has anyone replaced the Amal on a 348 with something else? I would like to hear how the conversion went. I can tell you that at moment it is not only the Monty fuming!!!! Quote Link to comment Share on other sites More sharing options...
feetupfun Posted August 8, 2009 Report Share Posted August 8, 2009 Difficult to diagnose over the internet but the first thing I thought of was that maybe for some reason perhaps associated with the work you had done on the carby, the fuel level may be too high in the float bowl. Possibilities are sticking float/float needle, bent/broken/cracked float arm, leaking float (float doesn't float as high). High fuel level can cause fuel to be lost out the float bowl overflow and/or into the motor as you ride, and will cause the motor to run rich. Quote Link to comment Share on other sites More sharing options...
belldane Posted August 9, 2009 Author Report Share Posted August 9, 2009 Thanks for that. Took the Amal out today and replaced it with the old Mikuni. The smoke has gone, however the jetting is all haywire. Do you happen to know if Amal and Mikuni pilot and main jet numbers correspond with one another? (ie if the Amal main jet is a 150, will the Mikuni 150 be the same) Today has convinced me that the Amal has something terribly wrong with it. The float level appears to be ok so is the needle and seat. I have heard of some poor casting on Amals which over a period of time can make them go haywire. I think there is some other problem in its innards. Anyway it's a start. Any idea where I can buy a jetted Mikuni for a 348? Quote Link to comment Share on other sites More sharing options...
feetupfun Posted August 9, 2009 Report Share Posted August 9, 2009 No I can't recommend any source for pre-jetted Mikunis. I bought a new "pre-jetted" Mikuni for a TY250 and spent many hours trying to get to run right and ended up giving up on it and rebuilding the standard carby. For the 348, I do want to try a KT250 Mikuni because they work well on both my KT and my 250 OSSA trials bikes, and being a piston port trials motor, I suspect the Cota 348 might also work well with the KT carby, but I haven't tried it yet. I suspect the reason the Mikuni you are trying on your 348 is not working well might be that it is jetted for a reed - valve motor. Quote Link to comment Share on other sites More sharing options...
helm Posted August 9, 2009 Report Share Posted August 9, 2009 hi had a mikuni on a beamish that had amal jets in it worth a try ,you also need to make shore vyou use a 2 stroke carb not a 4stroke one, also is the slide correct ? i would play with the mikuni a bit but only change one thing at a time cheers Quote Link to comment Share on other sites More sharing options...
nh014 Posted August 11, 2009 Report Share Posted August 11, 2009 Recently converted my 348 over to Mikuni and it now runs as good as ever or better than new (I've had the bike since 1977 adn competed regularily on it). Contact Sudco (www.sudco.com) and order a Mikuni VM26S / spec T/V, setup as follows: 120 main 35 pilot 2.5 slide 6F21 needle N8 needle jet Quote Link to comment Share on other sites More sharing options...
belldane Posted August 12, 2009 Author Report Share Posted August 12, 2009 Thanks for that. I can get a VM26 from the Estates for a good price. Is there a difference between the VM26S and the VM26? Also what is Spec T/V? Thanks again for the info. Very helpful Quote Link to comment Share on other sites More sharing options...
nh014 Posted August 13, 2009 Report Share Posted August 13, 2009 Beldane I do not know what the 'S' or T/V spec stands for. The Sudco catalog (available on their web site) may identify it. I do know that when I talked to Sudco's tech support, the VM26S T/V was what they recommended as a replacement for the Amal as used on the 348 Cota. It bolted right up and other than raising the needle one notch, it was spot on. Quote Link to comment Share on other sites More sharing options...
belldane Posted August 16, 2009 Author Report Share Posted August 16, 2009 Thank you all for your help. The problem turned out to be a bit of lint in the innards below the pilot jet. The previous owner had done an amazing job of polishing the Amal but had obviously forgotten about plugging up all those little holes before hitting the carb with the buffing wheel! It starts first or second kick now and it is great to ride. I would post a photo if I knew how to. I have looked at the procedure for doing so and you almost need to have a pilot's licence!! Thanks again. Those Mikuni settings I got will come in useful as I have another 348 under the house waiting to be looked at which came without the carb. Quote Link to comment Share on other sites More sharing options...
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