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CT70 Spark plug went bad after only 12 miles??

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I just recently rebuilt the top end with a new head, valves, cylinder, and rings. I have only ridden the bike for about 12 or 13 miles, and the plug went bad and was black full of carbon. Is that bad? 

I'm using 92 octane 10% ethanol fuel. C7HSA Spark Plug. But I have never had a spark plug go bad after such a short period of time. 

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Is the carbon dry or oily?

dry: forgot the choke on, main jet too big/fell out, float level incorrect, restricted air inlet, weak ignition system etc.

oily: burning oil / issue with the rebuild (oil control ring, valve seal, piston/cylinder sizing etc.

 

Is that the correct heat range plug (stock) for that engine?  (a #7 is actually pretty hot so shouldn't be the issue)

Beware of counterfeit NGK plugs sold on E-Bay, Amazon etc., hard to tell them apart from the real thing.

Always buy from a reputable vendor or dealership.

Edited by mlatour
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1 hour ago, mlatour said:

Is the carbon dry or oily?

dry: forgot the choke on, main jet too big/fell out, float level incorrect, restricted air inlet, weak ignition system etc.

oily: burning oil / issue with the rebuild (oil control ring, valve seal, piston/cylinder sizing etc.

 

Is that the correct heat range plug (stock) for that engine?  (a #7 is actually pretty hot so shouldn't be the issue)

Beware of counterfeit NGK plugs sold on E-Bay, Amazon etc., hard to tell them apart from the real thing.

Always buy from a reputable vendor or dealership.

Just rode 5 miles with a new plug going 25 to 30mph in my neighborhood. This is what the new plug looks like after 5 miles.

It looks dry except for the bend piece (don't know what its officially called), looks a bit shiny and I don't know why it has white there. The old bad plug was dry. And C7HSA is stock for this bike.

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I'd say more likely of an over-fueling problem than possibly ignition or oil consumption issues.

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3 minutes ago, mlatour said:

I'd say more likely of an over-fueling problem than possibly ignition or oil consumption issues.

Alright sounds good. That would make sense because I jumped from a 58 main jet to a 65 main jet, because I needed to rebuild the carb, and a 65, and 70 main jet came with it. I'll try a 60 main jet and see if that works better. My air mixture screw is half a turn from fully in.

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So I went back to the 58 main jet (stock), but I had to screw in the air mixture screw a lot. The air mixture screw is a quarter turn from fully in (that was about the same thing for the 65 main jet). Anyone know why this is? 

Edited by RedRockets_up_in_here_dude
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1 hour ago, RedRockets_up_in_here_dude said:

So I went back to the 58 main jet (stock), but I had to screw in the  mixture screw a lot. The air mixture screw is a quarter turn from fully in (that was about the same thing for the 65 main jet). Anyone know why this is? 

The main jet and mixture screw have nothing to do with each other. The mixture screw is for the idling end of the circuit. The main jet comes into play at nearly wide open to fully open throttle.

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16 minutes ago, 76xtdrvr said:

The main jet and mixture screw have nothing to do with each other. The mixture screw is for the idling end of the circuit. The main jet comes into play at nearly wide open to fully open throttle.

I heard somewhere that it's not very good for the air mixture screw to be so close to being fully turned in. I think he said that means you may need to adjust something? I don't remember if he said to try other pilot jets. Also when I set the idle right, with the air mixture screw about 1 1/2 turns out, the engine bogs when I try to rev the engine. The bogs go away when 1/4 turned out.

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25 minutes ago, 76xtdrvr said:

The main jet and mixture screw have nothing to do with each other. The mixture screw is for the idling end of the circuit. The main jet comes into play at nearly wide open to fully open throttle.

The main and pilot circuits are separate, but they DO overlap each other along the fuel curve. When I raised the needle (richened) on my pit bike project, it required me to lean the idle mixture screw and when I lowered the needle (leaned) it required (enriching) the idle mixture screw...

Edited by El Extremo
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4 minutes ago, RedRockets_up_in_here_dude said:

I heard somewhere that it's not very good for the air mixture screw to be so close to being fully turned in. I think he said that means you may need to adjust something? I don't remember if he said to try other pilot jets. Also when I set the idle right, with the air mixture screw about 1 1/2 turns out, the engine bogs when I try to rev the engine. The bogs go away when 1/4 turned out.

Honestly, I pay more attention to how the engine runs than the number of turns. If you can get good performance without being screwed all the way in, or backed all the way out, I would call it good....

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That stupid little carb drafts the pilot circuit through the main...It's dumb, but it's cheap.

Put the 58 back in it.

Set the fuel screw 1 1/2 turns out, get it started. Set the idle speed with the speed screw. THEN you can get the best idle/highest idle speed using the fuel screw. The reset the idle speed with the speed screw.

Assuming that's the stock carb that uses a fuel screw. Many of those had an air screw.  The procedure is still basically the same.

Nobody mentioned the year of the bike. As emissions laws came in, carbs began changing quite a bit.

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1 hour ago, Shawn_Mc said:

That stupid little carb drafts the pilot circuit through the main...It's dumb, but it's cheap.

Put the 58 back in it.

Set the fuel screw 1 1/2 turns out, get it started. Set the idle speed with the speed screw. THEN you can get the best idle/highest idle speed using the fuel screw. The reset the idle speed with the speed screw.

Assuming that's the stock carb that uses a fuel screw. Many of those had an air screw.  The procedure is still basically the same.

Nobody mentioned the year of the bike. As emissions laws came in, carbs began changing quite a bit.

Forgot to mention it's a 1974.

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If that' the original carb (CT70k1-K3) it actually does have a pilot jet. Should be a 35 and comes with an AIR SCREW as opposed to a fuel screw.

Screwing in, or closing the fuel screw enrichens the mixture. Out leans the mixture. Air screws seem to want start about 1.75 turns out, assuming the passages are all clean.

Adjusting is pretty much the same, although you may end up adjusting the idle speed screw more than once. Set the idle speed where it sounds right, then dial the mixture screw in or out until the idle speed is at its highest point. Then reset the idle speed with the speed screw. Go back and verify your mixture screw setting. The going back and fourth is the annoying part of an air screw on a tiny four stroke. It doesn't take much  air to run that tiny engine.

If the engine speed just keeps rising as you turn out the mixture screw, the pilot is too big.

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23 hours ago, Shawn_Mc said:

If that' the original carb (CT70k1-K3) it actually does have a pilot jet. Should be a 35 and comes with an AIR SCREW as opposed to a fuel screw.

Screwing in, or closing the fuel screw enrichens the mixture. Out leans the mixture. Air screws seem to want start about 1.75 turns out, assuming the passages are all clean.

Adjusting is pretty much the same, although you may end up adjusting the idle speed screw more than once. Set the idle speed where it sounds right, then dial the mixture screw in or out until the idle speed is at its highest point. Then reset the idle speed with the speed screw. Go back and verify your mixture screw setting. The going back and fourth is the annoying part of an air screw on a tiny four stroke. It doesn't take much  air to run that tiny engine.

If the engine speed just keeps rising as you turn out the mixture screw, the pilot is too big.

Ughhh. I tried your suggestion out and it still runs bad like before. It ran better with the 65 main jet. I tried number 1-4 in the throttle slide needle thing. Every time I accelerate the engine bogs down until I get into the higher rpms. Im thinking it could be the float? There is a dent in the float, but I set the float height to 20mm. It will idle fir a bit then it dies. It also revs high then low when it idles. It basically diesnt have a steady idle.

Edited by RedRockets_up_in_here_dude

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27 minutes ago, RedRockets_up_in_here_dude said:

Ughhh. I tried your suggestion out and it still runs bad like before. It ran better with the 65 main jet. I tried number 1-4 in the throttle slide needle thing. Every time I accelerate the engine bogs down until I get into the higher rpms. Im thinking it could be the float? There is a dent in the float, but I set the float height to 20mm. It will idle fir a bit then it dies. It also revs high then low when it idles. It basically diesnt have a steady idle.

Send pics of your needle grove and clip position...

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