Go engine b21 help
 

I bought a Caster zx1.5r, it came with a gotech b21. I put it in my losi 8b because i needed a motor. Blew my losi 350 last week and this seemed like a good replacement. I sealed it up before i installed it. It fired up good so i went ahead with tuning. Its got good smoke and runsaround 220-230. It has this habbit of blowing the plugs tho. The end of the plug is shiny and the coil is grey but its deformed and usually snaps the wire. I dont get it. Its making lots of power and temps are good. Fuel mileage is quite good but ive been through 3 plugs in the last 2 days. What could be causing this? Plugs are #6 cold from yeah racing. On a side note i put an hpi .25 in the caster buggy with the same plug and i didnt seal it. Ive been through 6-7 tanks on the same plug and that motor is fine. Same plug and same fuel.

Most times when an engine blows plugs it is too rich on the lsn and lean on the hsn. It will seem to run fine like this. Check the idle gap and set around .7mm or .030" easiest way to check is to pull the restrictor out and use a paper clip to set the carb slide opening width. If it is too wide you will need to lean the lsn and richen the hsn.
Also do not shut down an engine by plugging the exhaust if you are.

Rex

I never shut my cars off like that. It usually cuts out when its getting low on fuel....is that coincedence? I know they have a tendancy to go lean when low on fuel because of the lack of pressure in the tank. Maybe this is the case?

If it's tuned properly it should run strong right to the bottom of the tank.
I would follow Rex's (22Racer) advice and check the idle gap.

If it's too wide, you will be rich on the bottom and lean on the top as Rex suggested.
You will start off somewhat rich, then come in really hot and lean at the bottom of the tank in this situation.
Set the idle gap to .5 - .7 as suggested then don't touch it. Tune the bottom and around this idle gap, and tweak the top end as required.
Basically your setting your idle speed with the low speed needle.
If the idle is low - lean the bottom. If the idle is high - richen the bottom. This ensures a proper air fuel ratio for you to tune around.

You can juggle two needles quite easily, but trying to juggle three things at once can lead to mis-tuning and chasing your tail around in circles all day.

Give it a go. I'm sure you will find a good tune by getting the idle gap and low speed needle in harmony first.

I will try that. Thanks. I tore the motor apart last night thinking maybe i was getting dirt or possibly metal shavings in the combustion chamber and thats what was breaking the plug wire but it was clean as hell inside.
Ill set the idle gap as suggested and try tuning it that way. The motor is strong when its running so i hope this sorts out the issue, im starting to like this motor and im not interested in sourcing another one.

If it's still apart, check rod/crankpin wear.
Excessive rod clearance is also a condition that blows plugs.

Check the shim stack too. You should have .5mm worth of shims from memory.
Normally 1 x alloy .3mm and either 1 x copper .2mm or sometimes 2 x copper .1mm depending on year of manufacture.

Any less than .3mm may cause plug issues through over compression or maybe detonation if the motor is getting real lean towards the bottom of the tank - especially if the filament is deformed or pushed up into the plug body.

A cold plug is not ideal in these motors either. Most guys run medium or hot depending on fuel type.

Havent had a second to fire it up yet. I noticed shims on the head but i didnt take note of what was there. I never asked at the lhs but are head shims something that most lhs will carry?

Whats the recomended plug then? Ive had the best luck with OS #8 in my MT's also McCoy 059s were decent but that was in big motors (.32+).

Gotta get my starter box batts charged up and ill see if i can get her lit up.

We found nice results with O'Donnell 97T (now obsolete I believe) and the Werks #6 med or #5 hot. OS P4 or even P3 will work great too.

Not sure on the shim availability. Most .21 motors will run similar shims, so you should be able to get something to fit if you need it.
If it's a stock GO .21 it should have the .5mm worth of shims installed unless somebody has been tinkering :)

Arent os p3 and p4 plugs turbo head plugs? I dont think mine has the turbo head button.....it certainly didnt have a turbo plug in it when i got it and buddy said hes been running it that way for a while. How do i tell whether its a turbo head or not?

I think the blue head Go 3 port sport engines were std. plug. They also had an aluminum carb. They ran great, most other Go's had turbo plugs.

Rex

Ok good to know. Mines got a black head with a plastic carb. Its a bit better quality carb than some ive seen, still hate the plastic ones tho. So my motor is likely turbo head then? Guess i better stop running std plugs in it then lol

Look inside the plug hole to see if it had the taper below the thread to suit the turbo plug.

No taper just threads then nothing. Its a std plug head. Unless the guy before me took the turbo head button out? I cant see that tho.....he didnt seem to be the tinkering type

http://s1295.photobucket.com/user/BK...tml?sort=3&o=0

Theres a pic of the button. Looks std to me. Should i still go with hot plugs?

Also for shims there is a single silver/nickel coloured one and a single copper. Couldnt tell you what size they are. One of these days im gonna get a digital micrometer.