GG 80 Racing trouble with spark plugs

[Jack1710]

HI 

I was wondering if any of you had difficulties with spark plugs in GG 80 cc Racing 2018? I go through them quite often - sometimes every 2 hrs. Bikes runs great but spark plugs have tendency to die prematurely. Those sparks have rather dark colour that suggest rich mix, unfortunately carburetor has only front adjustment screw (at manifold ) for gas ratio only and not oxygen one. I run 91 Octane gas (only this is available here) 75:1 mix ratio at 800-900 above sea level - 2400feet. I am considering to get aviation fuel 100 octane, NGK BPR5ES. Kids are not reving this bikes at full throttle - this could be an issue too. 

I try to drop main needle and open gas ratio adjustment - bike didn't like it, I also cut fuel ratio by screwing in an adjustment gas screw - bike didn't like it, needle is in the middle. 

Has any one have similar issues and some good ideas how to stop replacing spark so often? 

Thank you 

[b40rt]

Is air filter clean ? Do not put to much oil in air filter as this will also make it run rich.

[rcgods]

Where are you getting the plugs from?  There are apparently a lot of fakes being sold on auction sites etc.

http://www.ngk-sparkplugs.jp/english/techinfo/fake/index.html

[Jack1710]

9 hours ago, b40rt said:

Is air filter clean ? Do not put to much oil in air filter as this will also make it run rich.

Yes, it is and I use very light oil K&N. 

[Jack1710]

8 hours ago, rcgods said:

Where are you getting the plugs from?  There are apparently a lot of fakes being sold on auction sites etc.

http://www.ngk-sparkplugs.jp/english/techinfo/fake/index.html

I buy them from Honda store. I do not think this is an issue. Thank you 

[arnoux]

These bikes are jetted way too rich from standard with the Dellorto PHBG 21 carby

Lift the clip on the needle to the top position. (so leaning the needle as much as possible).

You will find the pilot jet is size 50 standard. They are much better with 42.5 (45 is OK but still a tad too rich)

Main jet should be 100

This works perfectly with Australian fuel 95 Octane. 

 

Edited January 27, 2020 by arnoux

[Jack1710]

30 minutes ago, arnoux said:

These bikes are jetted way too rich from standard with the Dellorto PHBG 21 carby

Lift the clip on the needle to the top position. (so leaning the needle as much as possible).

You will find the pilot jet is size 50 standard. They are much better with 42.5 (45 is OK but still a tad too rich)

Main jet should be 100

This works perfectly with Australian fuel 95 Octane. 

 

Thank you very much. I think this will solve my issues. Thank you for your time and advice 

[Jack1710]

Carburetor issues due to rich fuel conditions may result in premature spark plug malfunction. 

 

I was recently working on a factory set up carburetor that caused rich mix conditions and premature spark plug failure in Central Alberta. Initially bikes were working flawlessly but then with colder temperatures and luck of high revving,  spark plugs were fowl  (black deposit of carbon), misfire and died. This resulted in bad spark plugs that have to be replaced on a regular base. 

Initially I tried to drop down slides’s needle,  but bike was very unhappy and bogging. I also tried to adjust petrol flow with gas screw adjustment - decrease gas flow but this also was no enough to decrease flow of gasoline. Your carburetor may have oxygen adjustment screw if is on a airbox side. Mine is on engine side therefore is a gasoline adjustment screw. 

After consultation with few of my colleagues I came to conclusion that Start jet aka pilot jet that works from 0-1/4 throttle opening needs to be adjusted first. With this particular Delorto carburetor I had factory pilot jet 50. I bought two additional pilot jets 45 and 40. After installation I put gas adjustment screw at 1 1/2 turn from closing position and started both bikes. Both bikes started very easy with choke. I also put brand new spark plugs to check color on the electrode tip after run test. 

I run both bikes for approximately 15-20 minutes and after reaching optimal engine temperature I have adjusted idle screw and adjust gas mixture. I have notice that bike with jet size 40 was running initially great but with opening throttle at traveling speed bike bogged and almost had tendency to stall. 

With jet size 45 bike was running very well. I had to open gas screw in carburetor to 3 full revolutions though with jet 45. Unfortunately jet 40 with 4 full revolutions wasn’t able to deliver enough of gasoline and was bogging regardless of my efforts when in motion. 

After run test I compared three spark plugs. 

Jet 50 was black and carbonated-  that is significant for rich bike conditions that will result in spark plugs failure (sometimes 2 hours of running time) and exhaust fill up with unburnt gasoline 

Jet 45 nice bronze color indicates great gasoline combustion and perfect temperatures conditions 

Jet 40- light ash color that indicated very lean conditions that if continue prolong running could result in ring and pistons failure - melting

To summarize: 

It is good idea to start with adjusting pilot jet with either gas or oxygen adjustment screw. If this won’t solve your issue - replace pilot jet.  All bikes, except fuel injected ones,  with carburetor are set up on sea level conditions where you have a lot of oxygen. Those bikes are shipped all over the world with variable elevation. If you live higher then 400 meters you will run into rich combustion troubles. My elevation is 850 meters above sea level. Bikes had extremely rich conditions that resulted in poor combustion and sparks plugs failures . 

 Obviously if I go to Baseline Mountain where elevation is 1700 meters above sea level I may be able to adjust gas flow with screw adjustment and cut fuel flow but I may also have to change to jet size 40.

 

Now: to get a little bit more spice to carb adjustment: 

If I need rich condition on my throttle from 1/4 to 3/4 I will raise needle up. If I need leaner condition due to higher elevation and axygen starvation I may have to drop needle.

If I need more gas from 3/4 throttle to full opening : I will put bigger main jet. Obviously with higher elevation I will put smaller main jet. 

 

The most interesting part is that all those elements working as a chain reaction: 

Pilot jet even though is considered to work from idle to 1/4 throttle is constantly meter/provide gas during 1/4 to 3/4 and full throttle operation. 

So playing first with pilot screw adjustment and then jet is critical. Do not jump to changing needle adjustment or main jet if you have problems with rich conditions at the bottom. Well, actually you can try to  drop needle and tight fuel adjustment screw first and see if your issues are resolved. If not get size smaller pilot jet if you have issues with fowl spark plug.

 

Also what is quite interesting: every jet gives carburetor certain amount of fluid per second or minute. If pilot jet is rich and you fully closed fuel adjustment screw this doesn’t mean that you cut completely flow of fuel. Pilot jet is still providing gasoline. Similar situation is when you exceeded three full revolutions to open fuel flow screw- you maxed out fuel intake and jet 40 (in mine situation) wasn’t able to give it more fluid and resulted in very lean conditions. 

Jet 50 with fully close adjustment screw was giving too much gasoline so I had to change to the next size jet 45 that was working very well. 

After changing to jet 45 the throttle was working well from idle to full power. 

I hope I gave you same idea how to solve carburetor issues with new bikes that are jetted -set for sea level conditions. 

JJ

 

 

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