read my plugs.

[Frogger]

just wondering what those with experience think about this.

the bike was running fine and one day it got a mid range flat spot then the next day it was back firing as i was slowing down and bliping the throttle to down shift. i figured its running rich but after taking the plugs out i found cylinder number 2 plug was buggered. the middle rod that connects to the spark plug lead had dettached from the plug itself. now with new plugs its running quite poor , normally under load. if im cruising there is no problem and it still back fires when i down shift and slow down.

the plugs show signs of being rich on #1 and lean at #4 and it leans out between the middle.

this picture is the best i can do atm but it gives a general idea.



are there well know reasons that would cause its to lean out across the cylinders ?

[B J]

Could be a very slight leak in the gasket were the pipes bolt to the heads maybe,

[Frogger]

its got a 4 into 2 exhaust system and each pipe has a hole with a nut on it on the bottem that gets blocked with a bolt. with the bolt in it back fires more then with it out. im about to check the airbox and see if its blocked but realy dont want to have to pull the carbs as the boots are a bitch to get back on.

[B J]

Boots could be leaking too

[agrid]

Spark plug reading with unleaded fuel is not as easy as the old days. I reckon you have a leaking boot on the far left

[roadtrain]

Possibly the - airflow temperature differential across and around the individual cylinders being different -
multiplied by the fuel delivery mechanisms physical delivery pathway to each inlet port -
divided by the economic expenditure (cost) outlayed per spark plug unit -
added onto the fact that maybe ya bikes shagged & you could go out a buy a brand new one (problem solved) -
two upsides being -
1) brand new bike makes for an easy ride -
2) no stressing over - what the?? - is screwin with me spark plugs

[Frogger]

the 2 leaner carbs have a slight patch on the outside where the boots attach and dust has gathered. so i guess thats the leak. but i thought if there is a leak the carbs go lean and the way this thing is back firing would seem its rich.

[agrid]

Back firing through the carbs is one thing, popping through the exhaust is another and indicates a lean condition, probably an air leak around the boot.

[darkfibre]

What sort of bike?

While you are tinkering, have you got a compression gauge?

Comp test and valve clearance test before anything else can be a good idea if its an older bike.

You can spend a lot of time tinkering with carbs with no result if there is mechanical problems.

[Frogger]

its a yamaha zeal 250 "fxr"

i pulled the carbs and found alot of shit in there due to the carb boots coming off slightly and allowing air to get in unfiltted. the airbox and boots on this thing are pretty shit. u can only open the airbox from the bottem and to get the boots on its almost impossible without the top of the airbox off . would be easier with pod filters but that just makes more head aches in the end.

[Desmo]

Get some starting fluid such as "start ya bastard" and spray it around your boots and carbies.
Should be able to hear it run smoother if/when you spray it on the leak.
Don't ride it or you'll risk putting a hole in your piston or burning a valve, your far left is very lean.

[Frogger]

yeah i have a zxr250 piston with a hole in it that sits on my desk as a reminder lol , it idles fine its more the mid range it would have a flat spot

[GSX IN SHED]

Hey Frogger... what happens to the way she runs ?
1. When you apply some choke?
2. Bring the revs up slowly with throttle? ( no load)
3. Ride with load and apply some choke?

[g0zer]

its got a 4 into 2 exhaust system and each pipe has a hole with a nut on it on the bottem that gets blocked with a bolt. with the bolt in it back fires more then with it out. im about to check the airbox and see if its blocked but realy dont want to have to pull the carbs as the boots are a bitch to get back on.

the airbox is common to all pots so unlikely it is causing a lean condition to only some pots

have you tested compression like df said? there is no point doing anything with it until you confirm compression is the same across the bank.

[Frogger]

its going ok now , i pulled the carbs gave them a quick clean and adjusted the floats slightly to make it abit richer. after putting it all back on i found it wasnt running properly and noticed #2 header pipe was cold and after looking the spark plug leads are shit. i have like 1.5 meter of new spark cable but its different it has like a string in the middle rather then a wire like the stock ones , and its slightly fatter.

should i get some more cable but with the wire inside or is it all this new string stuff.

[agrid]

The string stuff is modern carbon leads. I think its worth replacing them all but the lean condition on the left cylinders says air leak to me.

[GSX IN SHED]

hey Frog.... if ur keen... go with the carbon leads.. ( u won't fuck up the awesome picture on the 51'' plasma Santa got for me, when you ride by).
I just did a set for GSX. (Dyna) If u can Grab a mate with a multi meter..Check when you make the leads...when you fit the caps, and just once more after fitting 'em..( just pull em all off an' check resistance one more time..) 5000 ohm / 300mm ....rough guide... OK?
good luck.. bro.....
(use WD40 spray on all plastic/rubber bit ( with running) This is easiest way to find split/ crack/air leak between carbs' and barrel....rev's will change....yeh?

[Frogger]

oh realy , i stopped watching tv because it was to unstable with all the scooters that ride around here lol .

im almost 100% sure it was a mixture of an air leak , dirty carbs and bad connetion on the spark plug. the carb boots were old and hard and even after boiling them i had trouble fitting the airbox last time so i had to remove the top part of the airbox to get them on but it screws together from the bottem which cant be accessed when its connected to the carbs so i put the top on and put some hot glue in spots to hold it on, but it didnt hold up by the looks of it.

[inertia]

Could be dirty jets, inbalanced carbs or so many things. How does raising the float level make it any richer when the jet sizes and needle taper control fuel flow?

[g0zer]

Could be dirty jets, inbalanced carbs or so many things. How does raising the float level make it any richer when the jet sizes and needle taper control fuel flow?

if there is no fuel level there is no flow, if the level is too high the motor fills up with fuel. float level is the single most important factor in balancing fuel flow across a carb bank.

the rubber boots are vibration isolators for the carbs, when they age and harden it is bad for fuel level control.