June 12, 201115 yr I have just purchased a Montesa 348 which appears to be fitted with a Dellorto VHBZ carb as opposed to the original (i believe) Amal. This got me wondering, how interchangeable carbs are and how does changing the carb change the behaviour of the bike? Any knowledge of this subject would be of interest as the previous owner purchased the carb off of ebay and I am wondered if a different carb would change the characteristics of the bike.
June 12, 201115 yr Your correct in thinking it should be an amal carb I have a 349 cota and they come fitted with a mk11 2627 concentric, I believe your bike would be fitted with the same but not absolutely sure. Strangely enough I was going to ask the same Question. If a carb is jetted up correctly for a given bike is any one carb better than another? I have been told that Amal carbs are no good as they are worn out after Six months, is this correct or is someone just trying to sell me a carb? Lets hope we both get some answers to our quetions.
June 12, 201115 yr Author Have just noted that the carb also has no choke. The shaping of the carb body suggests that it is capable of taking one but where the choke lever would normally be is what appears to be a blanking plate. Any thoughts...
June 15, 201115 yr The Amal MK2 concentric was the standard carb for the bike and they do wear out in the slide area because both the slide and the material it slides in where made of the same material. I had my carb re-sleeved with a harder material than the slide, put in a new slide and the problem was solved. All up around 70 dollars Australian which was cheaper than to buy a new carb or fiddle about trying to make a replacement carb work properly.
June 15, 201115 yr Amal slides wear in 15 years i've changed two so thats about 15 tyres to one slide so insignificant really. keep the carb clean use an air filter properly ( cleaned after every trial etc and you'll help your carb last) the OEM carb was chosen because it worked for a price, there may be alternatives but how much time and money will you spend chasing that nirvana when an established product is readily available.
June 16, 201115 yr I am not a big fan of the later model Amals, I think the early models were better but tend to wear the slide as already mentioned, my experience when changing my '85 montesa from the amal to a keihn increased the performance, seemed like almost 2 more horsepower for some reason, both carbs were properly jetted and ran well, I believe changing to a modern carb is the way to go, delotro or mikuni seem to be the most popular, not sure abought your absence of a choke...pull the block off plate to see if there is a fuel passageway to add one.
June 16, 201115 yr Author Choke sorted, the assembly was all there just well seized. Stripped and re-assembled and working fine. Fuel leak not a good story though.....thought it was the filter/washer but the thread that secures bowl that connects the petrol pipe to the carb has a stripped thread! Tried to tighten it and out pops a helicoil! What to do now ?
June 17, 201115 yr Choke sorted, the assembly was all there just well seized. Stripped and re-assembled and working fine. Fuel leak not a good story though.....thought it was the filter/washer but the thread that secures bowl that connects the petrol pipe to the carb has a stripped thread! Tried to tighten it and out pops a helicoil! What to do now ?
June 19, 201115 yr Many Many moons have passed since I was on anything with a Bing or Amal, yet these things did work at the time. The Japs really took things to a new level with the Mikuni and the Kiehin, just better fuel metering devices. More sensitive as well. The Dellorto PHBL works good in 26mm version for a standard fitment for many bikes, not finicky, it just works , and may be the modern option for old bikes, yet as mentioned, the OKO is now available(Kiehin copy) on the cheap and in 24,26,28, sizes to accomodate different displacements of motor, and taste. Jetting varies due to displacement, but these things do work well with a bit of polish!
June 20, 201115 yr I've just bought a brand new 28mm Oko from a scooter shop for £50.00. A chap I know who runs a 349 cota with an Oko carb on is going to give me the correct jetting for it, once I get the information I will gladly pass on the details to you. If you could post your findings in this thread that would be great. Edited June 20, 201115 yr by firedfromthecircus
June 23, 201115 yr Here's the carb settings for a 349 cota with a 28mm Oko carb Main jet 110 (Keihin) Pilot jet 38 (Keihin) JJH needle (middle groove) No 5 slide Also worth checking float bowl height, (should be 19mm) These settings were kindly sent to me from a chap who Knows a lot about 349 cota's I hav'nt had chance to try these setings out myself yet as the bike is now in bits having a referb. Knowing how thorough this chap is It should give anyone a good "benchmark" setting to start from, let me know how you get on.
June 24, 201115 yr Here's the carb settings for a 349 cota with a 28mm Oko carb Main jet 110 (Keihin) Pilot jet 38 (Keihin) JJH needle (middle groove) No 5 slide Also worth checking float bowl height, (should be 19mm) These settings were kindly sent to me from a chap who Knows a lot about 349 cota's I hav'nt had chance to try these setings out myself yet as the bike is now in bits having a referb. Knowing how thorough this chap is It should give anyone a good "benchmark" setting to start from, let me know how you get on. Cheers bud.
July 7, 201115 yr I had my carb re-sleeved with a harder material than the slide, put in a new slide and the problem was solved. All up around 70 dollars Australian which was cheaper than to buy a new carb or fiddle about trying to make a replacement carb work properly. belldane can you tell me who did the job on your Amal?
July 7, 201115 yr Keychance. Yep. Allan Graham, 145 Jenkins Street, Douglas Park, NSW, 2569. Phone 02 4632 7202. Mate I really hope he is still kicking because he did a great job on my carb. See Ya
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