max Posted March 3, 2011 Report Share Posted March 3, 2011 Hi all, I wonder if you could help me with my 2 questions below... 1) I am currently finishing the full restoration of a model 150 Sherpa T 250 and got the engine running today after installing the (new style) electronic ignition from Dave at Bultaco UK. The bike starts, idles, revs and runs really nicely - the problem is that when i blip the throttle the revs don't drop back to idle as quickly as i would expect. After each blip, the revs drop gradually, slowly settling back to normal idle - it may only take 1-2 seconds, but it doesn't seem quite right to me. - I have had the engine fully re-built by the guys at Bultaco UK, so it should all be sound - The throttle seems to snap back fast enough so it doesn't seem like it is an issue with the throttle - The throttle slide/carb body seems in good nick visually - I have checked there is no air leak at the carb/airbox Has anyone experienced anything similar or can anyone suggest anything? Throttle cable needing lubing perhaps? 2) What VHT paint do people use to paint exhausts? In my experience exhaust paints can be a bit rubbish and chip/scratch with the slightest touch or knock OR ruin the finish with a drop of petrol or oil? Any tips/advice for how to paint an exhaust that looks nice and lasts more than one outing would be great? Many thanks in advance, Max Quote Link to comment Share on other sites More sharing options...
zarkoff Posted March 3, 2011 Report Share Posted March 3, 2011 Hi all, I wonder if you could help me with my 2 questions below... 1) I am currently finishing the full restoration of a model 150 Sherpa T 250 and got the engine running today after installing the (new style) electronic ignition from Dave at Bultaco UK. The bike starts, idles, revs and runs really nicely - the problem is that when i blip the throttle the revs don't drop back to idle as quickly as i would expect. After each blip, the revs drop gradually, slowly settling back to normal idle - it may only take 1-2 seconds, but it doesn't seem quite right to me. - I have had the engine fully re-built by the guys at Bultaco UK, so it should all be sound - The throttle seems to snap back fast enough so it doesn't seem like it is an issue with the throttle - The throttle slide/carb body seems in good nick visually - I have checked there is no air leak at the carb/airbox Has anyone experienced anything similar or can anyone suggest anything? Throttle cable needing lubing perhaps? 2) What VHT paint do people use to paint exhausts? In my experience exhaust paints can be a bit rubbish and chip/scratch with the slightest touch or knock OR ruin the finish with a drop of petrol or oil? Any tips/advice for how to paint an exhaust that looks nice and lasts more than one outing would be great? Many thanks in advance, Max hi you say you have checked the carb to air box have you checked the carb to engine, sounds a bit like it is getting air in somewhere which can give the same problem. Quote Link to comment Share on other sites More sharing options...
max Posted March 3, 2011 Author Report Share Posted March 3, 2011 hi you say you have checked the carb to air box have you checked the carb to engine, sounds a bit like it is getting air in somewhere which can give the same problem. Hi Zarkoff, Yes i checked that by spraying a little easy start around the manifold/carb/airbox and the revs were not affected. I normally use this trick as the the revs should rise if there is an air leak. The manifold is on pretty tight from carb to manifold and manifold to head. Any other way of checking if air is getting? Cheers, Max Quote Link to comment Share on other sites More sharing options...
zarkoff Posted March 3, 2011 Report Share Posted March 3, 2011 how about the carb jetting the wrong pilot jet can give this problem also, i have just fit a new carb to my honda and when trying different pilot jets the same thing was happening ( running weak) at one point. Quote Link to comment Share on other sites More sharing options...
woody Posted March 3, 2011 Report Share Posted March 3, 2011 If it is still running the original Amal carb, the slide/body may be worn, even if it looks ok. It would be fortunate now to still have an original Amal in good working order and without wear, given the hours it will have done. May be worth trying a new slide. If the body isn't too worn it should stop it (if that is the problem of course, but worth a try for the cost of a slide) Quote Link to comment Share on other sites More sharing options...
max Posted March 3, 2011 Author Report Share Posted March 3, 2011 how about the carb jetting the wrong pilot jet can give this problem also, i have just fit a new carb to my honda and when trying different pilot jets the same thing was happening ( running weak) at one point. Jetting is standard and this problem was not apparent before the engine strip and rebuild. Somehow, it doesn't feel like a jetting problem. Quote Link to comment Share on other sites More sharing options...
max Posted March 3, 2011 Author Report Share Posted March 3, 2011 If it is still running the original Amal carb, the slide/body may be worn, even if it looks ok. It would be fortunate now to still have an original Amal in good working order and without wear, given the hours it will have done. May be worth trying a new slide. If the body isn't too worn it should stop it (if that is the problem of course, but worth a try for the cost of a slide) Hi Woody, It is still running the original Amal carb. The bike has only done a genuine 187 miles would you believe (it has been my fathers since new) I am thinking it may well be the carb/slide body. Would it help to give the slide a light rub with 1400 (or higher) grit wet and dry to make sure it is as smooth as can be, do you think? Or is there anything you can use to lubricate the motion slightly? I am happy to buy a new slide, but wonder if it is worth trying anything first? AND any suggestions or tips for VHT paint for exhaust? Thanks all. Max Quote Link to comment Share on other sites More sharing options...
pschrauber Posted March 3, 2011 Report Share Posted March 3, 2011 Hi Woody, It is still running the original Amal carb. The bike has only done a genuine 187 miles would you believe (it has been my fathers since new) I am thinking it may well be the carb/slide body. Would it help to give the slide a light rub with 1400 (or higher) grit wet and dry to make sure it is as smooth as can be, do you think? Or is there anything you can use to lubricate the motion slightly? I am happy to buy a new slide, but wonder if it is worth trying anything first? AND any suggestions or tips for VHT paint for exhaust? Thanks all. Max The main bearings of the crank where changed too and are installed proper? You can try out your easy checking method at leat on the ignition side. To the paint job, I have personal got good result with good heat resistand paint from the can when the silencer was blasted so no rust or old paint was left. After application you should wait until the paint is really dry and then store the parts in an oven or "heat chamber" for some hours. Ask your lokal paint shop if they can do the paint job and heat threatment for you. You will notice that the paintsurface of a heat treated exhaust is still dull but has not the same rough surface anymore which is normally typical for this heat resistance paint when applied. By the way don't apply the paint when it is too cold, best temp. is around 20 Quote Link to comment Share on other sites More sharing options...
tomtom385 Posted March 3, 2011 Report Share Posted March 3, 2011 Hi Max, How yer doing, Have you thought of powder coating the exhaust. i saw a powder coating system at a kit car show that looked ok, nearly bought one for powder coating bits on my resto project. not sure of the durability. electrostaticmagic diy powder coating. Has anyone used this system, it looked great at the show. Regards, Tom, Quote Link to comment Share on other sites More sharing options...
max Posted March 3, 2011 Author Report Share Posted March 3, 2011 The main bearings of the crank where changed too and are installed proper? You can try out your easy checking method at leat on the ignition side. To the paint job, I have personal got good result with good heat resistand paint from the can when the silencer was blasted so no rust or old paint was left. After application you should wait until the paint is really dry and then store the parts in an oven or "heat chamber" for some hours. Ask your lokal paint shop if they can do the paint job and heat threatment for you. You will notice that the paintsurface of a heat treated exhaust is still dull but has not the same rough surface anymore which is normally typical for this heat resistance paint when applied. By the way don't apply the paint when it is too cold, best temp. is around 20 Quote Link to comment Share on other sites More sharing options...
max Posted March 3, 2011 Author Report Share Posted March 3, 2011 Hi Max, How yer doing, Have you thought of powder coating the exhaust. i saw a powder coating system at a kit car show that looked ok, nearly bought one for powder coating bits on my resto project. not sure of the durability. electrostaticmagic diy powder coating. Has anyone used this system, it looked great at the show. Regards, Tom, Hi Tom, Not doing bad thanks mate... apart from a frustrating day in the garage. One step forward and all that... How are you - have you re-claimed your garage yet? I would definitely give powder coating a go, but am trying to stay as close to original as possible. I think my issue is not letting the VHT paint cure/bake on the bike? I'll re-paint and keep my fingers crossed. Cheers, Max Quote Link to comment Share on other sites More sharing options...
pschrauber Posted March 3, 2011 Report Share Posted March 3, 2011 Hi there, Yes, main bearings were changed - it was by Dave Renhams engine builder, so i would assume it was done correctly. Your exhaust looks good. What brand do you use? (I use Halfords and i am not convinced) Mine always look like that until they get a drop of oil/grease/petrol on them and then they are stained. Is that because they have not been cured do you think? The surface does stay rough. This time I tried over coating mine with VHT lacquer, which looked great, but today spilled petrol on it and it came off in seconds - very annoying! I think i will see if i can spray them again and the get them baked (they will not fit in my oven!) or fit to the bike VERY carefully and bake them in situ. Thanks, Max Have used POR15 once with best results but this paint is very pricey and difficult to apply, the paint here is from a supplier for professional workshops "Werkstatt Bedarf" in Germany suppose to be resistant up to 600 Quote Link to comment Share on other sites More sharing options...
tomtom385 Posted March 4, 2011 Report Share Posted March 4, 2011 Hi Tom, Not doing bad thanks mate... apart from a frustrating day in the garage. One step forward and all that... How are you - have you re-claimed your garage yet? I would definitely give powder coating a go, but am trying to stay as close to original as possible. I think my issue is not letting the VHT paint cure/bake on the bike? I'll re-paint and keep my fingers crossed. Cheers, Max Hi Max, nah, no garage yet, hopefully get the base down this summer. can see your having probs with the exhaust paint. have you got a heat gun. not as quick as an oven, but effective i believe. cheers, tom, Quote Link to comment Share on other sites More sharing options...
copemech Posted March 5, 2011 Report Share Posted March 5, 2011 Slow return to idle is usually a partly blocked pilot jet. Might have disturbed a slight bit of dirt while off, as this just started. Quote Link to comment Share on other sites More sharing options...
max Posted March 5, 2011 Author Report Share Posted March 5, 2011 Thanks for all your replies guys. Today I removed the carb, blew through all jets with the compressor (again), inspected the throttle body and slide (which both looked fine), re-fitted and re-set the pilot screw (fully in and 1.5 turns out). I kicked it over, blipped the throttle a few times and it returned to idle fine - nice and quick and nice and clean. My guess is that it was a partially blocked pilot, hence the slow return to idle, but i am just glad it is running properly again. Thanks all for your input. Max PS - it seems PJ1 (Satin Engine Case Paint, not their exhaust paint) is the best paint for bully exhausts, if you don't have the facility for high temp curing! Quote Link to comment Share on other sites More sharing options...
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