1997 GTI 720 Blowing Plugs

[dgiles]

Hello all

I'm new to this forum. I have a GTI 720 single carb that has no power seems to get worse as it warms up. We replaced all the grey lines (all 20 feet of them) rebuilt the carb, compression 135 MAG and 132psi PTO. Seems like the engine loses all engine response as you go over 30mph. Then as you come back to idle the engine starts to missfire and stalls. Restart after a few minutes same thing misses and won't get out of its own way. Now the kicker is put in two new NGK plugs and the engine sounds great works great then after about 15min of WOT the same senerio misses and won't rev. The plugs look like they are burning or getting some sorta coating??? oil inj is still on and has new gas. Now my question could this be a coil problem? I thought the engine was getting lean but the plugs are black not oil, like if you had them in a fire. Why are the new plugs correcting the problem? but only temporary?

thanks in asdvance for any advice

 

[kustomkarl]

I would do a compression check to see what is going on inside the engine.
You'll need a compression tester. Go to Auto Zone. I think they sell for like $25.00. The compression gage, will screw in the cylinder head in place of the spark plugs. To test compression, remove both spark plugs. Place spark plug caps on the plug cap studs near the cylinder head to ground the empty caps. This completes the circuit of the ignition electrical system and prevents any electrical problems from the caps being un grounded. Using the correct adapter for the threaded end of the tester,( same length of the spark plug threads length)screw in the tester in one plug hole. Hold the throttle wide open. Push the start button. Watch the compression gauge, when it peaks out at the most compression, let go the start button. Read the psi number. I would do it 3 times to be sure it is accurate. Check both cylinders the same way. The ideal compression is 150 psi per cylinder. If it is less, it's not a problem as long as they are close to being the same. If the psi is less than 90 it might need be time for a tear down and a rebuild. If the psi in 1 cylinder is say 140 psi and the other is 80 psi you need to tear down and repair. This difference is a lot and there is a problem. I hope this helps you.

Karl

 

[timmyboy76]

set the carb to these settings........1997 GTI 717 1.5n/s 23 - 43psi LOW- 1 HIGH- 1-1/2....1.5n/s is your needle and seat, inwhich it should pop in those specs,23-43psi, any higher/lower, motor/carb wont work right...

 

[dgiles]

I did over carb if I can remember the low mixture screw is 1.5 turns out and the high mixture is 0 completly turned in would this be correct Thanks for your help

 

[timmyboy76]

no ,factory specs calls out what I posted earlier...

 

[dgiles]

Thanks Timmyboy76 so 0 on the high speed mixture screw is not 0 turns out than? I had to remove the adjustment for high speed to change one of the o-rings and did not count the out turns. Then I was reading that 0 was the high speed adjustment assuming 0 was 0 turns out and low was 1.5. turns out!

Thanks

 

[timmyboy76]

hey...yah. 0=0 turns out, bottomed out. That would be the starting point, bottom the high speed screw, then turn ur out 1.5 times. Same with low speed, start with it bottomed out, and turn ur 1 out...:cheers:

 

[dgiles]

Thanks

I will try it tommorow at the lake and let you know

Thanks