mralex714 Posted May 19, 2015 Share #1 Posted May 19, 2015 After rebuilding the carbs the engine has a "thump" sound from the intake and exhaust. This thump is also felt in the seat. In addition to this it doesn't seem as peppy as before. Any thoughts on what to check? Link to comment Share on other sites More sharing options...
cowpuc Posted May 20, 2015 Share #2 Posted May 20, 2015 It always amazes me how smooth our V-4's can run on 3 cylinders - they can be deceptive - where it really shows is huge power loss (Tweeks came to me on 3 - owner rode her for years like that - even enough power on 3 that he was happy). I would spit check the headers on each jug after idling a couple minutes just to see if its coming up on all 4. If you havent recently swapped new plugs in her, she may have a dead one that is firing once in a while - enough to cause a "thump" feeling as you are describing. These 10mm plugs really dont to like to even be blackened from a little over choking... Thats where I would start anyway.. Link to comment Share on other sites More sharing options...
Patch Posted May 20, 2015 Share #3 Posted May 20, 2015 :bowdown:It always amazes me how smooth our V-4's can run on 3 cylinders - they can be deceptive - where it really shows is huge power loss (Tweeks came to me on 3 - owner rode her for years like that - even enough power on 3 that he was happy). I would spit check the headers on each jug after idling a couple minutes just to see if its coming up on all 4. If you havent recently swapped new plugs in her, she may have a dead one that is firing once in a while - enough to cause a "thump" feeling as you are describing. These 10mm plugs really dont to like to even be blackened from a little over choking... Thats where I would start anyway.. Link to comment Share on other sites More sharing options...
mralex714 Posted May 20, 2015 Author Share #4 Posted May 20, 2015 It always amazes me how smooth our V-4's can run on 3 cylinders - they can be deceptive - where it really shows is huge power loss (Tweeks came to me on 3 - owner rode her for years like that - even enough power on 3 that he was happy). I would spit check the headers on each jug after idling a couple minutes just to see if its coming up on all 4. If you havent recently swapped new plugs in her, she may have a dead one that is firing once in a while - enough to cause a "thump" feeling as you are describing. These 10mm plugs really dont to like to even be blackened from a little over choking... Thats where I would start anyway.. You are correct one cylinder is not firing. I pulled the plug for that cylinder and it was dry but does have a good spark. I relly don't want to pull these carbs again Link to comment Share on other sites More sharing options...
Patch Posted May 20, 2015 Share #5 Posted May 20, 2015 Have you thought about letting it run on straight sea foam? Not my preferred way but might free the blockage? You would know if it worked by monitoring the temperature. I would leave enough in the bowl for an over night soak. Patch Link to comment Share on other sites More sharing options...
Donvito Posted May 20, 2015 Share #6 Posted May 20, 2015 Each carb has a drain screw. You could open it on the carb that isn't firing to see if it's getting gas if you haven't already. Stuck float? Link to comment Share on other sites More sharing options...
mralex714 Posted May 20, 2015 Author Share #7 Posted May 20, 2015 Each carb has a drain screw. You could open it on the carb that isn't firing to see if it's getting gas if you haven't already. Stuck float? I just came in from doing that and there was fuel in the bowl. Link to comment Share on other sites More sharing options...
jdog910 Posted May 20, 2015 Share #8 Posted May 20, 2015 if you have a timing light that works great to see if spark is present, ive used it many times. beets taking things apart to check Link to comment Share on other sites More sharing options...
flyday58 Posted May 21, 2015 Share #9 Posted May 21, 2015 You are correct one cylinder is not firing. I pulled the plug for that cylinder and it was dry but does have a good spark. I relly don't want to pull these carbs again If it's sparking AND dry, sounds like a no-gas condition, even if there was some fuel in the bowl. Vito may be right, float could be hung up. You could try rapping on the carb with the butt end of a wooden hammer handle or similar, if you haven't already. Did you take any pics of the rebuild you could post? Maybe we could spot something. Link to comment Share on other sites More sharing options...
Patch Posted May 21, 2015 Share #10 Posted May 21, 2015 I would try this: Fill the bowl through the drain, take a peak inside the barrel you want to completely immerse the float, meaning over filling, usually you see some back flow into the barrel when this happens! Then rap on the bowl, if that won't free it the removing the cap is next. Link to comment Share on other sites More sharing options...
mralex714 Posted May 21, 2015 Author Share #11 Posted May 21, 2015 Yesterday I put some Gunk fuel system cleaner and filled up and drove home about 15 miles. Today I went for a ride and still runinig the same.. While going 65 there is a slight hill. I give it a little throttle to maitain speed and bang the engine came to life with the exceration I was use to. Link to comment Share on other sites More sharing options...
mralex714 Posted May 26, 2015 Author Share #12 Posted May 26, 2015 Yesterday I put some Gunk fuel system cleaner and filled up and drove home about 15 miles. Today I went for a ride and still runinig the same.. While going 65 there is a slight hill. I give it a little throttle to maitain speed and bang the engine came to life with the exceration I was use to. Got excited to soon. Went for a ride today and the bike stumbled when giving it throttle. I got to my destination about 6 miles and checked the pipe of the cylinder that wasn't firing before and it was barley warm. Looks like those carbs will need to come back out, looks like I did something wrong. Link to comment Share on other sites More sharing options...
Patch Posted May 26, 2015 Share #13 Posted May 26, 2015 " Looks like those carbs will need to come back out, looks like I did something wrong." I think that is the right thing to do, while it's off make sure the pilot circuit is completely clean on that one carb. I have had to pull fresh carbs before as well, it can happen to anyone! Patch Link to comment Share on other sites More sharing options...
Silverado6x6 Posted May 26, 2015 Share #14 Posted May 26, 2015 On a hill it came to life? Float needs to be adjusted. Link to comment Share on other sites More sharing options...
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