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Spark plug CR7E instead of CR8E (due to availability)?

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Hello, can one run CR7E instead of recommended CR8E? CR8E cant be obtained locally and have to be ordered online = have to wait which I prefer not to. 

The bike runs unsmoothly, quite noticable when giving steady throttle at cruise speed, I can feel power surges and power losses, like hickups every few seconds. Very annoying. Recently changed oil+filter, changed carb float bowl needle. I presume it is spark plug because it feels just like when a spark plug is bad - any other ideas please share.

Its a DRZ400SM with MRD/SSW, 3x3 and soon fcr39.

Regards

Edited by Hugh Dick

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6 minutes ago, ohiodrz400sm said:

You mean CR7E?

Yes! updated description

6 minutes ago, ohiodrz400sm said:

Does it start out ok and get progressively worse as you ride?

It might, have not noticed but will make sure to check next time.

6 minutes ago, ohiodrz400sm said:

Did you gap it prior to installation?

I did not, still have previous owner's spark plug in it.

 

Myabe I'll gap it and make sure its as residue free as I can make it, meanwhile onlineorder a CR8E?

I did have carb out and float bown apart, maybe something happened there? I put 95 octane in.

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What your describing is lean surge , motor is running out of fuel(or proper mixture) so it misses firing cycles or the mixture is burnt out before it creates the correct pressure(power stroke). The bike feels like your dragging a brake . At steady speed it's a combination of needle clip position , needle taper, and main jet size.

 

There is a rich mixture surge as well that feels different , generally the motor is really missing and rough running , surge feels more like giving it some throttle, and then releasing, giving throttle, releasing, ect... Tailpipe will be black soot covered , rear fender ,light, licence plate may also be black covered.

 

.

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1 hour ago, jjktmrider said:

so it misses firing cycles or the mixture is burnt out before it creates the correct pressure(power stroke). The bike feels like your dragging a brake

Yes this is the feeling! It feels like it misses a cycle and dies for a fraction of a second and engine-breaking, then picks up with power again, creating annoying yo-yo like driving. This was why I presumed bad spark plug. This might be an illusion - but it feels like the pick up has more power, almost like it misses a burn cycle and then have more fuel/air for next stroke - this might be an illusion though.

1 hour ago, jjktmrider said:

At steady speed it's a combination of needle clip position , needle taper, and main jet size

It's a DRZ400SM with stock carb, I presume needle has only 1 clip position and stock taper - I have not double checked this, so maybe previous owner did a shim thing. Annoying to check. Main jet size is 160 from previous owner (double checked).

  • Is it possible to fix such issue with fuel/air mixtrure screw? Have not fiddled with it at all.
  • Maybe air leak, but feels like it would run like crap all over, if at all.
  • When running on choke (alleviate lean condition?) it has too high idle. Did not try cruising with choke. On twostrokes it's easy way to check if lean, but they are completely different, I don't have so much experience with fourstrokes.

?

Regards

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Trying to run on choke with these can't be done because they don't have a choke as your used to (me too) your old 2T's choke just added fuel , with this carb it has an "enrichment circuit " meaning it add fuel AND air to "enrich" the mixture , PITA for testing . If you have the stock carb jetting and added the MRD and 3x3 mod you MUST rejet . You added a lot of airflow but nothing was done to add more fuel to go with it . I imagine it is a royal pain to ride at steady throttle , she must be surging like a rodeo bull.

You need to get the JD Jetting kit with a bigger pilot jet , adjustable needle and bigger main jet . However if your getting an FCR soon I may not be worth it . For just a short time to get you by till you get the FCR you can just by 1 pilot jet and one main jet and shim up the stock needle to get you at least close .

IIRC a #42 pilot will do but can't remember what the stock main would be to go one size bigger , hopefully someone will chime in with it .

You can crank out the mixture screw about 2 turns more to give you some extra fuel down low for now , just make sure it has some spring tension so it doesn't fall out while riding.

 

.

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Cool man, thanks for informative reply! =)

I have a feeling previous owner did some of the "mandatory" stuff, 3x3 mod was done as well as 160 jet instead of stock. Pilot jet I did not check when carb was open, but was smart to photograph the stuff for future reference! Is this the wrong pilot? It says 5,25 (?!) or 5,29 - see attached pic.

Quote

You can crank out the mixture screw about 2 turns more to give you some extra fuel down low for now

Yes, it runs rodeo style on low throttle, when giving more gas it disappears - hopefully its just a matter of screwing to make her happy (!).

Can it damage the engine or can it stall dangerously on highway cruise? If No, I will just live with it until I get the FCR =)

 

Capture.JPG

Edited by Hugh Dick

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Cool man, thanks for informative reply! =)

I have a feeling previous owner did some of the "mandatory" stuff, 3x3 mod was done as well as 160 jet instead of stock. Pilot jet I did not check when carb was open, but was smart to photograph the stuff for future reference! Is this the wrong pilot? It says 5,25 (?!) or 5,29 - see attached pic.

You can crank out the mixture screw about 2 turns more to give you some extra fuel down low for now

Yes, it runs rodeo style on low throttle, when giving more gas it disappears - hopefully its just a matter of screwing to make her happy (!).

Can it damage the engine or can it stall dangerously on highway cruise? If No, I will just live with it until I get the FCR =)

 

Capture.JPG.3d98c637a2a199e916c3912685514884.JPG

 

Look at the attached photo. I think you're​ looking at the wrong jet. Also, the pilot is supposed to be recessed in the hole, not sticking out like the starter jet.Screenshot_20170409-100223.png.5338587954ead0a7fff2db64c794b8aa.png

 

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I'm betting it's the carb, not the plug.

For the record, lean engines experience incomplete combustion, which is why lean engines tend to backfire and stackfire. Seems counter-intuitive, because it is. You would expect less fuel to burn faster, but it doesn't because lean patches in the combustion chamber stymie the flame front, which is also why lean engines show raw hydrocarbons when monitoring emissions with an infrared analyzer.

 

 

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7 hours ago, ohiodrz400sm said:

Look at the attached photo. I think you're looking at the wrong jet. Also, the pilot is supposed to be recessed in the hole, not sticking out like the starter jet.

Aha, so pilot jet is wrong type I presume - is this the correct one, 25 i guess? https://www.24mx.se/lagfartsmunstycke-mikuni-kort-1 

2) Can I change it by just removing float bowl without removing entire carb? (I have allen screws)

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39 minutes ago, ohiodrz400sm said:

Looks like it
Yes

Great!

I cant find the mixture screw, does this carb have one? I have googled and image-googled to no avail :(

 

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1 minute ago, ohiodrz400sm said:

It's in the picture I posted. There may be a brass plug over it.

Aha the "This is where I drilled"-circle. Yes in mine there is a brass plug. I could drill it out but would have to remove carb, which I'm in no hurry to do before FCR39-swap. I will put in 25 pilot jet of the correct type and hopefully it will help a bit until I swap carbs, or I will just live with it =)

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If the 25 pilot don't help, you could shim the needle up a bit, which helped mine, but my real cure was to vent the carb up into the still air under the tank. I was able lean the needle out and have not had that surge return.

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4 hours ago, bucket list said:

vent the carb up into the still air under the tank

What does this mean? I have a hose going from the carb into the air box boot nipple - is this what you mean?

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5 hours ago, Hugh Dick said:

What does this mean? I have a hose going from the carb into the air box boot nipple - is this what you mean?

No, I'll try to get a picture of it tonight, but it's left side of carb near the top, right behind the choke knob. You have to get a longer hose and run it up into a place where the wind and swirling air can't effect it.

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