Is there any way I could have messed up the compression test? It pulls really hard before and after the flat spot! This makes no sense at all..

 

Sure, it's possible. I'm thinking you'd have to do it wrong pretty consistently. What was the method you used? All spark plugs removed? Battery in good condition for turning the engine over? Turned the engine over 5+ times for each measurement? Try a different gauge, maybe it is not working.

 

All spark plugs out ready for some new NGK and coils, mate this is odd! Gonna see if the cylinder head needs torquing down some more, might have missed a couple bolts who knows. Hopefully this cheap compression tester is junk!

 

Ok so I have an update on this useless thread NEVER BUY CHEAP COMPRESSION TESTERS FROM EBAY. Absolutely useless and will have you going down a dead end and cost you time and money. They were out because the joints leaked.

Took my F3 for a dyno run to see if the sniffer could tell me anything about fuelling and if it was all **** about tit. The graph showed the midrange to be dripping rich and I should try smaller jets. He recommended 128 130 130 128 main jets to start with and run from there. This is obviously WAY smaller than stock 135 138 138 135 so due to these Black Widow Headers they have created a super rich condition but it is probably coupled with the airways in the carbs being partially blocked and/or the pipes flowing much easier and the stock air filter not drawing enough air through. Will try smaller jets and update everyone later this week!

 

You can see the huge dip in the mids because of all that fuel

 

Obviously a freer flowing air filter would make more sense but they’re very expensive compared to a few main jets..

 

Easier to read. Yes, jets are less expensive and K&N is certainly proud of their air filters, lol. 83 hp at the rear wheel is very respectable for a 26 year old bike.

 

Thankyou @idodirt! not bad at all for a scabby old CBR eh. The chap at the dyno said he could fish quite a few extra ponies out of it with a tune up too, its just gotten all out of whack over the years through faffing and idiots like me having a pop at mechanics.

Just want to say thankyou to everyone and your replies and help, learnt more through this than anything else.

I would recommend a Dyno run if you're stumped about a crappy hole in your power after a new exhaust or faffing with your own carbs!

Until next time...

 

Semantics idodirt, yes/no, its about expectations both given and recieved of which we'll agree on from different angles. Good point about clips though, hondas need shimmed and everything wants tuned

I've not been on in a while so hope its been resolved, That's awesome that you went and got a dyno run, the guys suggested jet sizes are dubious though, i suspect he'd lead you down a rabbit hole.

​​​​​Was just thinking, when you dyno'd was it still shimmed? That would explain it being too rich in the mid. Another thought was it's worth removing the baffle or fitting one, some exhausts are picky about that.

My open shorty flattened out my midrange so much that it felt like vtec kicking in when it pulled through to wide open before i set the carbs up.

​If it wasnt shimmed when on dyno somethings a miss, exhaust blockage, needle wear / a seal etc or something causing overfuelling, could be worth trying another set of carbs to rule them out

Could be you've too big a washer form.

I'd suggest if you havent already,

1. standard needle height and a baffle.
Or
2. Shimming with form B (0.5mm) washers. So add a form b to each needle with the factory washer still in place.

Best to measure n' match closely 4 washers as tolerance is +/- 0.05mm ish on form B washers but thats just best practice. Should've specified before, my bad.

Carbs can be really tedious to get right but there could also be an underlying issue leading you astray.

if you're in the uk stick to e5 super unleaded and if you're in scotland i could possobly lend you a hand to diagnose/setup.

Cant remember if i said but 'stage 1' jetting on an open exhaust/std filter is

​​​138/140/140/138
Needles shimmed 0.5mm, 1mm if necessary.
Air mix 2 turns out is base but can need tweaked.

​​​​Hope something there helps if its not already resolved

 

Hey Iamhiding thankyou so much for your input and sharing your experience! I was having a wee gander at my timing which was a tooth off after my manual CCT came loose and taking the cam journals off it was snapping bolts left right and centre (maybe not enough oil on the threads last time) and they're broken off in the cylinder head! For f**ks sake. I think its time it went in the bin really, its taken all my money and time and effort and have had little in the way of mechanical victory.

The jets the dyno guy recommended worked a lot better with a pipercross air filter but the flat spot was still there in the higher gears, starting to think its something more sinister like you said.. the shim was a 0.5mm washer at the time of the dyno plus 138 140 140 138 main jets and it was draining a tank in no time its just not getting enough air but the more i faff the more down the hole it goes! It would be worth the trip to Scotland just to get some pointers in the right direction!

Even with the pilots at 1 turn out the choke was almost redundant on start up, its all such a mess! Would a carb balance be in order?

Taking this thing to a garage would probably be in excess of £800