spitting back through carb

Russell · Post by **Russell** » Mon Aug 31, 2009 3:25 am

Hi all
I have just finished rebuilding my Darmah SSD which I purchased last year. On starting the engine it fired first go and I was very pleased but as the engine revs rose to around 2800rpm it spat back through the front carb, this will not go away. The bike has new coils and plugs, the heads have been off and the valve shims have been done. Ignition timing has been checked with timing disc and the advance is working o/k. Crank pickups checkout o/k for resistance and wires o/k with no shorts. New carbs are fitted (40mm) the old ones were 40mm and it spit back with these. Could this problem be down to worn valves and guides as they did have some wear in the guides. It always spits back at around 2800 rpm.
Your advice would be of great help as I struggling now to find the cause.

MartinMille BANNED · Post by **MartinMille BANNED** » Mon Aug 31, 2009 5:31 am

Have you tried changing the ign boxes form front to rear to see if they might be the problem?

Lumpy · Post by **Lumpy** » Mon Aug 31, 2009 5:39 am

Maybe quickest and easiest check Russ is the intake manifold gasket. These deteriorate and allow it to suck air and lean off the mixture, they are also very easily over tightened and squeeze out.
However I would be surprised if thats the issue. It sounds like timing to me. My SS had a spit back through the carb issue. It would do it at idle, very randomly and stall itself. I persevered with it for a time until some other issues arose that I`ve gone into in other posts and was forced to address it. Basically it turned out to be the pick up wires. According to the multi-meter test these wires were fine, no shorts, no current leakage to each other, no nothing. I went in there in desperation as i could`nt find anything else. Cut the outer cover off and the insulation on the individual wires fell apart.
In short i`m trying to say don`t trust the multi-meter and if these are the original wires then I would be getting rid of them as they will cause issues sooner or later. I`m a big fan of ditching the original wires, maybe because of the head-aches they caused me when they failed as oppossed to how easy it is to splice in new ones.

Russell · Post by **Russell** » Mon Aug 31, 2009 6:23 am

Thanks for the advice. Forgot to mention that the igniter boxes have already been swapped and it still spit back. The wires from thr pickups have already been changed when I got the bike but I do not know how long ago. I think for peace of mind I will change them as I have a length of pickup wire from steve which I ordered just in case.

Post by **BevHevSteve** » Mon Aug 31, 2009 5:05 pm

Hey russ - please see in the carb and fuel section the topic I posted regarding carbie sync..... They really need to be spot on.

Also p-up wires of course as we have previously discussed..

The intake manifold insulators a likely culprit as well as ex gaskets but I assume you changed them when you did the motor? Regardless it is very important to draw a fine flat file across the intake manifold to assure flatness and not overtighten the securing nuts.

To check if there is a leak there, get the bike warm go outside, wear eye pro and give a small squirt of carbie cleaner around the intake insulator.

If the revs go up a bit then drop back down voila you have found the problem. Do the previous flatness check and install new ones.

Let us know how she goes