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0-60mph 10 seconds. I don't know what else to try!!

  • Thread starter Thread starter capnjim
  • Start date Start date
C

capnjim

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I'm at a complete loss right now.
Here's the deal:
1978 GS750. I have been reading cliffs great site over and over again.
I have done all of the recommended procedures, airbox sealing, new O-rings, new intake O-rings, cleaned dipped carbs (They are spotless inside!). Valve adjust..
When I first got the bike it had melted airbox boots. I changed them and it was running amazing! I then had a coil die on me and I put in new 3ohm coils. It ran great for a while, but now not so much.
The strange part is, there aren't any obvious symptoms. It starts great, idles great, runs up to redline smooth...but, its a lot slower than it has been.
I have the fuel mix screws at 1.25 turns and have been playing with the idle mix screws for a while but I just can't get her to scream the way it was before.
Its like I only have 1/4 throttle, anything more makes no difference. From 1/4 to WOT has zero effect.
The plugs are light tan and it does seem a bit lean, but the air mix screws don't seem to help.
It will run the same on prime...just seems like its not getting enough fuel. I don't think its the needles or jets as it was running well for a bit with them at their current setting.
Could it be ignition? It starts right up and no backfiring so the timing seems good. Can you hook up the coils wrong but still have it running OK??
I'm stumped!!
 
Hard to say. I'd start at the beginning and verify spark (points, condenser, plug wires, etc), the carbs (any mods), and compression (how long since your last valve adjustment?).

BTW, why did you choose 3 ohm coils with points? Or has the ignition been upgraded? Points require 4-5 ohm coils.
 
capnjim said:
I'm at a complete loss right now.
Here's the deal:
1978 GS750. I have been reading cliffs great site over and over again.
I have done all of the recommended procedures, airbox sealing, new O-rings, new intake O-rings, cleaned dipped carbs (They are spotless inside!). Valve adjust..
When I first got the bike it had melted airbox boots. I changed them and it was running amazing! I then had a coil die on me and I put in new 3ohm coils. It ran great for a while, but now not so much.
The strange part is, there aren't any obvious symptoms. It starts great, idles great, runs up to redline smooth...but, its a lot slower than it has been.
I have the fuel mix screws at 1.25 turns and have been playing with the idle mix screws for a while but I just can't get her to scream the way it was before.
Its like I only have 1/4 throttle, anything more makes no difference. From 1/4 to WOT has zero effect.
The plugs are light tan and it does seem a bit lean, but the air mix screws don't seem to help.
It will run the same on prime...just seems like its not getting enough fuel. I don't think its the needles or jets as it was running well for a bit with them at their current setting.
Could it be ignition? It starts right up and no backfiring so the timing seems good. Can you hook up the coils wrong but still have it running OK??
I'm stumped!!
Click to expand...

If you are finding no love above 1/4 throttle, your needles and/or main jets probably need some love. I understand you have a stock setup (airbox, 4-2 exhaust). Where is the needle clip set? What mains are in there?

Do a plug chop at about 1/2-2/3 throttle to see what the needle circuit is doing. Then try one at WoT to see how your main is performing.
 
The bike is bone-stock. It was running great at one point, so i can't see it being the needles or jets.
I put in the three ohm coils as I have a Dyna ignition i am going to install. I was told by the salesman at Z1 that they would be fine with point until I did the dyna.
Could a "weak" spark cause it to run this way?
There is no backfiring, and it starts right away.
I'll have to do a few more proper chops. I inspect my plugs after most rides and they always look nice and tan.
Valves were done a month ago.
The ten seconds is approximate...it me sitting on the bike counting as I slowly watch the RPM's and speed climb to 100km/hr.
Its about as quick as my '95 Camry.
It runs and sounds great..if you took it for a test ride and didn't try cranking it you would think it runs 100%. Just nothing above 1/4 throttle.
 
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Have you tried running it without the air filter element to see if it effects the upper throttle ranges?
 
OK, you have changed coils. Could be important.

The stock coils are 4-5 ohms, meaning they will draw about 3 amps when fed with 14 volts.

Your new coils are 3 ohms, meaning they will draw almost 5 amps when fed with 14 volts.

You still have points. The reason the stock coils had a higher resistance was to limit the current through the points.
You are forcing more current (more than 50% more) through the points than they were designed to handle.

I would suggest doing a very close inspection on the points and condensors, then ordering up the Dyna kit as soon as practical.

But the plug chops are a good idea, too.

Are you absatively, posilutely SURE you have the wires back on the correct plugs? :-k


.
 
If the plugs look okay (I would think they would be super rich if it's a coil issue) then I would try checking the carbs again. It's very possible that they somehow got blocked by some gunk from the tank and are starving the bike of fuel. Also, if you have an in-line filter then take it off immediately. When my inline filter got blocked (it looked fine but wasn't) it felt like I had almost no power once off the pilots.

Check your petcock too, it could be going bad and not supplying enough fuel too.
 
Don't worry about the 3 ohm coils.. Until you install a Dyna Just hook up a ballast resistor to the 12v line to the coils use a 70's vintage Mopar ballalst resistor
My 850 has been like that for years

Yes check the fuel flow, make sure the fuel hose is as short as possible, no kinks. If you have a dirty tank ? You may need to clean the carbs again..
 
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My tank is clean (The petcock filter is spotless). I have a feeling it might be electric. I do have a new Mosfet R/R and I have my dyna ignition. I'll try to get them in this week.
I can't see it being dirty carbs. It just runs way too smooth and consistent.
 
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