weird starting problem on 87 gn sigma

[revhead072010]

hey guys, got a weird starting problem on an 87 gn sigma, its started doing it recently, will go out after it sitting over night to start it, engine turns over and sounds like no compression at all, then it seems to sound like it builds the compression up eventually fires, runs and idles like crap, then clears it self up back to smooth running after about a minute, then fine to drive, no problems at all on re starting all day, then left over night and next day does it all over again, it has oil filled to max, all other fluids are fine, its got me stumped lol thanks in advance

[Sigmaproject]

Sounds like you electric choke is out of whack if it is only a problem on a cold start. Try pumping the gas pedal 3 or 4 times before you wind it over. The carby's on the unleaded model are basicly sealed so that you cannot tamper with them.

[d3v147]

I think Magna EFI is less complicated than the abomination of a carby that comes on the GN!

[zabatron]

Sounds like wax pellet which controls automatic choke is sticking at start up and then freeing itself as motor warms up.Try resetting auto choke by depressing accelerator pedal to floor and then releasing it before starting engine.May also be worth spraying a small amount of Wd40 or similar lube spray on wax pellet actuator rod and on choke flap.

[revhead072010]

Thanks guys will try that when I go to start it tomorrow, would that cause it to also sound like no compression when cranking? Thanks again

[Sigmaproject]

If it is cranking over fast ..giving the impression of no compression..it is because the motor is not attempting to start. Similar to pulling out the coil lead and then cranking it . This is tied in with you fuel issue.

[revhead072010]

Hey thanks guys I did the full throttle trick after that reply was done went out yesterday and she fired up normal did a compression test anyway and all cylinders are around the 180psi mark

[revhead072010]

Oops just jinxed it lol went out tonight after it has been sitting for 20hrs and it did it again so as I was turning the key to crank I kept pumping the pedal till it fired does anyone have a link to the gn workshop PDF as the one in search post from 2009 doesn't work thanks heaps again I assume it's to do with the choke still

[revhead072010]

hey guys, went and had a look today before i started it and this is how the choke is when cold, i believe this is meant to be fully closed? and also would the cog have anything to do with it? and once warmed up opens fully fine, again to get it to start i had to keep pumping while cranking

choke closed
[img=http://s24.postimg.org/5761cejox/IMG_3498.jpg]

cog looks mashed
[img=http://s24.postimg.org/pm7417s4x/IMG_3519.jpg]

[img=http://s24.postimg.org/bv2mz0375/IMG_3522.jpg]

choke fully open
[img=http://s24.postimg.org/x60739lbl/IMG_3509.jpg]

[zabatron]

Choke flap should be fully closed when engine is cold,,that white nylon/plastic gear with the worn/broken tooth is what closes/opens the choke flap...might be a good idea to replace it.Also,if you have to pump accelerator a few times to get it to start,you may also have a split accelerator pump diaphragm

[revhead072010]

hey, put another cog thing on it from an old gk carby i had laying around last night, went out tonight and this time choke was fully closed yay, but still had to pump accerator to start,but when it starts is sounds like its missing a cylinder for the first 15 or so seconds seconds then it clears, i have swapped over the coil for a known good working one, and this week ill be changing the plugs to see if that helps, when i have the aircleaner off and the choke is open, if i get someone to pump the accelrator i can see a squirt of fuel go in.. is that what the pump diaphram does? cheers

[zabatron]

Yep thats what the accelerator pump diaphragm does..another symptom if it is split is a flat spot on acceleration.

[revhead072010]

yep on take off it has a ever so slight flat spot ... now how hard are they to change lol

[zabatron]

very easy to change...just undo 3 screws,remove cover and withdraw and replace accelerator pump diaphragm...just be careful not to lose the spring.

[revhead072010]

Thanks I'll tackle it when I get a free chance this week and update once done cheers

[revhead072010]

Just an update changed the plugs and now starts and runs smooth again thanks for your help