Author Topic: 1970 750four #2 #4'cylinders staying cold (Read 1390 times)

tomgrubb71@gmail.com · « **on:** April 16, 2015, 02:14:47 PM »

This bike has been gone over, everything refreshed from top to bottom, an carbs rebuilt, an synced, but when bike starts up an you rev the motor it back fires the same time you throttle it? An I have good blue fire on all wires an plugs, can somebody help with this issue!

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Airborne 82nd · « **Reply #1 on:** April 16, 2015, 03:15:55 PM »

Quote from: tomgrubb71@gmail.com on April 16, 2015, 02:14:47 PM

This bike has been gone over, everything refreshed from top to bottom, an carbs rebuilt, an synced, but when bike starts up an you rev the motor it back fires the same time you throttle it? An I have good blue fire on all wires an plugs, can somebody help with this issue!

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This sounds like a lot but does not say anything you did. So did you do the work? How did you sync. the carbs explain. Tell us how you did the 3K service.

tomgrubb71@gmail.com · « **Reply #2 on:** April 16, 2015, 03:52:53 PM »

No i didn't do the main engine work, but did do the carb sync, I used sync gauges bought from eBay , hooked them up on all the vacuum ports on the front of the carbs, engine was up to temp when sync took place, all throttle adjustments an slides was matched, then was checked a second time, after all was tightened, air screws an floats have all been replaced an set to specs, low an high jets was all cleaned an checked for any stale gas an dirt, points an condenser have not been replaced because, I checked them an they have no signs of scaring an have also been set to specs, all new spark plugs an wires have been installed, although these things have been done, I do feel that my problem may be an electrical issue, because of two cylinders having issues at the same time.

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Retro Rocket · « **Reply #3 on:** April 16, 2015, 03:59:06 PM »

I agree, check the points on the 2 and 4 side and also check the coil and connections going to those cylinders...

scottly · « **Reply #4 on:** April 16, 2015, 04:02:00 PM »

Check which spark plug wires go where: 1&4 go to one coil, and 2&3 go to the other coil. Sounds like you swapped the 2&4 wires.

BobbyR · « **Reply #5 on:** April 16, 2015, 04:13:55 PM »

tomgrubb71@gmail.com · « **Reply #6 on:** April 16, 2015, 04:30:07 PM »

Ok I may be just a little confused on the spark plugs, I have them plugged in as they come off the coils 1234, is this correct?

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scottly · « **Reply #7 on:** April 16, 2015, 04:32:16 PM »

No, should be 1,4 2,3

Vinhead1957 · « **Reply #8 on:** April 16, 2015, 05:01:38 PM »

Many times people have the connection wires shorted to the points base. The blue wire feeds the 1/4 cylinder coil. The yellow 2/3 cylinder coil. When the point set is open there should be no continuity to the base. It is very easy to turn the wire connection so it touches the base inadvertently. When the points are closed that wired set should have continuity to ground.

scottly · « **Reply #9 on:** April 16, 2015, 05:05:15 PM »

If it were a points issue 1 and 3 wouldn't be firing, either.

BobbyR · « **Reply #10 on:** April 16, 2015, 05:12:10 PM »

Quote from: scottly on April 16, 2015, 05:05:15 PM

If it were a points issue 1 and 3 wouldn't be firing, either.

This is true. Best guess is swapped wires. You could have a situation in which those two carbs are not getting gas.

tomgrubb71@gmail.com · « **Reply #11 on:** April 16, 2015, 05:16:02 PM »

Ok the wires coming out of the coils do not have the little number tags on them anymore, so sitting on the bike starting left to right is is 1423the way they would be labeled Scottly?

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scottly · « **Reply #12 on:** April 16, 2015, 05:20:14 PM »

Correct.

tomgrubb71@gmail.com · « **Reply #13 on:** April 16, 2015, 06:13:50 PM »

Ok so if it's running an I apply the choke a little bit, shouldn't they kick in an run? BobbyR

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tomgrubb71@gmail.com · « **Reply #14 on:** April 16, 2015, 06:15:37 PM »

Thanks Vinhead1957

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tomgrubb71@gmail.com · « **Reply #15 on:** April 16, 2015, 06:21:09 PM »

Just need to know which wire coming out of each coil goes where cause they're not numbered. Sitting on the bike the second cylinder from the left an the forth one all they way to the right are both staying cold

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tomgrubb71@gmail.com · « **Reply #16 on:** April 16, 2015, 06:25:06 PM »

Ok thanks Scottly

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scottly · « **Reply #17 on:** April 16, 2015, 06:28:45 PM »

The #1 cylinder is on the left, sitting on the bike. The coil that is connected to the working #1 should have the second plug wire connected to cylinder #4, the outer cylinder on the right side.

tomgrubb71@gmail.com · « **Reply #18 on:** April 16, 2015, 06:33:06 PM »

Right I understand, im getting great fire on all the wires, but they are not in right order lol

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tomgrubb71@gmail.com · « **Reply #19 on:** April 16, 2015, 07:19:22 PM »

Ok scottly I changed them around, wow! What a difference my friend, thanks everyone for your help, it's a success

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scottly · « **Reply #20 on:** April 16, 2015, 07:26:53 PM »

You're welcome.

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Author Topic: 1970 750four #2 #4'cylinders staying cold (Read 1390 times)