Bike has 0 power under load when under 4000rpm?

[Cmarino]

Okay so I did a compression test and here's what I found. 1 - 110 2- 105 3- 101 4- 118. I'm not sure if that's low enough to warrant the issues i'm having, someone advise please.

Here's the craziest thing I found; the spark plug on cylinder 3 was literally a different spark plug, it was DR8EA as opposed to D8EA. That's what I get for trusting autozone I guess, I was very, very surprised that I didn't notice when gapping and installing. The cylinder was still firing before, but it's definitely a bit better/smoother now.

Chuck; I remember you saying that 2 of my needlejets were different and you drilled them out to the proper size. Something I've noticed is that once moving at low rpm's in first gear(lets say 2000rpm, where youre barely moving), the bike will accept gas so long as it's just where the throttle is first engaged, so you're able to stay coasting and moving (slowly) without a problem. The issue is that it bogs when engaging the throttle anymore than that if it's under like 3500rpm. Do you think this could be the because of the needle jets?

As for the oil, I did change it while I was working on the bike, so maybe that could be the problem? I put in the amsoil dominator motorcycle oil. But I'm not sure if it's a clutch problem because if the clutch was slipping, wouldn't it still rev up and just not accelerate?

[Cmarino]

And as a reminder because there seems to be some confusion, bench and vacuum sync were just done, the bike starts fairly easily and idles perfectly, has no problem accepting gas in neutral or with the clutch in, and rides great above 3000rpm. Everything is completely stock, and I feel that there are no airleaks, I have new intake boots o-rings and airfilter and everything is set well and very much tightened down

[pdqford]

Here's the craziest thing I found; the spark plug on cylinder 3 was literally a different spark plug, it was DR8EA as opposed to D8EA. That's what I get for trusting autozone I guess, I was very, very surprised that I didn't notice when gapping and installing. The cylinder was still firing before, but it's definitely a bit better/smoother now.?

Howdy neighbor ;-)

How do all the spark plugs look color wise?

Has the tank and intake fuel filter ever been cleaned.

Are you running an in-line fuel filter?

[pdqford]

And as a reminder because there seems to be some confusion, bench and vacuum sync were just done,

Which carb sync tool do you use?
And at what rpm did you do the sync?

[Cmarino]

Howdy neighbor ;-)

How do all the spark plugs look color wise?

Has the tank and intake fuel filter ever been cleaned.

Are you running an in-line fuel filter?

I can insert a picture of the plugs later today and I'll take a video of how the bike runs tomorrow to make it more clear for everyone, but for now the plugs are black on the metal and a slight dusting of black on the ceramic; no tan anywhere, just black/white. Mixture screws are 2.5 out

Carb sync was done at a local shop so I'm not sure of the specifics, I didn't want to buy the tool so I had them do it.

Brand new petcock with no fuel filter, my old petcock seems pretty clean so I'm not worried about the tank, replaced because it was backfeeding into the vacuum line

[chuck hahn]

BR is the NGK race version of the B8 plug. And according to the parts fiche 2 of the MAIN JETS were wrong so according to the chart below i did use number drills and made them all the same. you got my number..call me.

https://www.jockeyjournal.com/threads/keihin-dynojet-mikuni-jet-size-cross-reference-tech.64769/

[chuck hahn]

According to the service manual (page 3-9) standard compression on a WARMED UP engine is 142 to 199. With a LOWEST LIMIT of 100. IF you arent doing the compression check with the throttle wide open redo the test. IF you did have it wide open then your compression numbers as posted indicate its time to rebuild that top end. Also the parts fiche says the main jets are #110.

By rebuild i mean measure bore wear per service manual too...not just throw new rings on the pistons

[Grimly]

BR is the NGK race version of the B8 plug.

The R there in an NGK denotes that it's a resistor plug, but NGK do a range of racing plugs. Istr an odd R in some plug types that did denote Racing use, but what make it was, I don't recall.

https://www.ngk.com.au/technical_info/racing-spark-plugs/

[chuck hahn]

An email from NGK directly stated its their race series that replaces B8ES,that how i remembered it. i think the thread was about NGK rumor about going out of production. May revisit tat thread to read the response to the inquiry i sent them

EDIT.. I STAND CORRECTED. It does denote a resistor plug.............

https://www.thegsresources.com/_forum/showthread.php?261324-Ngk-plug-shortahe&highlight=spark+plug+shortage

[Cipher]

According to the service manual (page 3-9) standard compression on a WARMED UP engine is 142 to 199. With a LOWEST LIMIT of 100. IF you arent doing the compression check with the throttle wide open redo the test. IF you did have it wide open then your compression numbers as posted indicate its time to rebuild that top end. Also the parts fiche says the main jets are #110.

By rebuild i mean measure bore wear per service manual too...not just throw new rings on the pistons

have the valves been set to spec. Cant seem to see that anywhere

[jimfish]

I have a 82 gs750 with the exact same problem it used to be a perfect running bike until the previous owner cleaned the carbs. Broke the pilot jet off in no4 and had to put a new carb on. I found 2.5 turns out on the mixture is good. starts perfect throttle doesn't hang no back fire. From what i have read on your post it has to be a carb issue as it is the only thing that made this bike run bad. Will be interested how you get on.

[zed1015]

The R there in an NGK denotes that it's a resistor plug, but NGK do a range of racing plugs. Istr an odd R in some plug types that did denote Racing use, but what make it was, I don't recall.
https://www.ngk.com.au/technical_inf...g-spark-plugs/

You are correct.
The code for an NGK racing plug starts with an R but confusingly they also have a range of race plugs that end EG.
The R in BR denotes a resistor plug.

[Rijko]

Okay so I did a compression test and here's what I found. 1 - 110 2- 105 3- 101 4- 118.

According to the service manual (page 3-9) standard compression on a WARMED UP engine is 142 to 199. With a LOWEST LIMIT of 100. IF you arent doing the compression check with the throttle wide open redo the test. IF you did have it wide open then your compression numbers as posted indicate its time to rebuild that top end. Also the parts fiche says the main jets are #110.

By rebuild i mean measure bore wear per service manual too...not just throw new rings on the pistons

Why is that, Chuck ?
Ofcourse i agree #3 @ 101 is not high, but still within service limits.

But if performed on a cold engine that would mean compression is higher.
And if performed with throttle closed, also means compression is higher.