Right my car is doing my nut right in!!

My car 1.8 zetec zx9r carbs and megajolt. When u drive it gently with the throttle it will rev ok, not good but ok. When u put your foot down more it bogs down about 2000rpm and will no go anymore. If you ease it passed there it will rev. If you floor it it just bogs.

Now iv tried so many different maps etc its got to be the carbs. Now they were set up by boggs and its done this all along. It had 190 jets in and iv now put 155's in. Its a bit better but still bloody gutless. I havent got adjustable needles so what do i do next? Smaller jets still or get some adjustable needles??

Also it wont rev past 4k.

This is really doing my head in. I went out in it yesterday and up a hill could get no more than 30.

I have a set of twin 40's sat here i was gonna sell, Im so tempted to rebuild them and put them on and see what happens but really want to use the bike carbs!!

Heelp please im going mad.

are the slidey things moving ok?
i remember years ago i had a mini with SU carb, took all the oil out the damper, and it did the same thing.
are the rubber diaphrams alright?

Dan,

I had this same problem
with mine.It differs on being a
pinto with zzr1100 carbs but
the syptoms are the same.
I found that the panel
filter was causing the hesitation
above 3000 rpm and the jets
were too small.I changed from
1.5's to 1.6's and it now goes
like stink.I have adjustable jets
and have them on the second
from the top notch.Try putting a washer
under each needle to lift the jets a touch.
Also check the diaphrams are sealed.
Andy

Ditto checking if the pistons are moving....

If they all move cleanly then it's very likely a jetting problem. To sort that out you ideally want to have access to a wideband lambda sensor so you can actually tell what's happening when it bogs down....

Shimming the jets will richen the mixture at mid-throttle. It'll either make it better (if you're running too lean) or worse (if you're already running rich)!! Another way of checking out what is happening is by using a colortune. Obviously you can't do this with the car moving (so you won't be able to assess the engine under load) but it'll tell you what the mixture map is like...

im using zx6 carbs and absolutly no running problems and when getting the jets right it would still run, would have thought the 190 jets you started with with were massive, ive not got any idea about megajolt but if you sure map and advance ok sounds like something basically wrong with carbs as on 155's even if mixture out would expect it to at least rev through the rev range, has it ever ran ok? if so must be some thing gone wrong, start with may be an idea to follow through from fuel supply, diaphram's, carb balllance etc. then i think you need some sort of lamba mixture sensor to correct mixture as trial and error be hard, a just got a basic gauge and narrow band lamba to do mine, i also sure zx9 carbs have adjustable needles is ther not groves with clips?
hope you get it sorted, finally would be good if you could check the megajolt on another care to eliminate that bit

if it was set up by boggs, and been doing it since, i'd take it back to them first

Has the car ever run right, so how do you know your ign map is ok

190's seem very large, is that what boggs put in?? I would go back to the default megajolt 2d map and try that and then I would raise the jet sizes in .05 increments upto about 1.60 - 1.75 ballpark area.

What colour are you plugs after a thrash, does it pink or run on.

Time for a bit of trial and error i'm afraid no quick fix I don't think.

Have a couple of beers everytime it doesn't work after adjustment, then you'll either get it right or won't care if its still wrong at the end of the day!!

Best of luck

Rich

Are you using the air filter they were set up with?
Bike carbs can be fussy about the airflow across them and can be unhappy without an airbox

Dan,

A few questions!

Have you ever run an AFR meter on it?
Do you have somewhere to bolt in an AFR wideband sensor?
What colour are your plugs after a good run?

The reason I ask is that my car behaved exactly the same as yours (except mine bogged down at around 4000). Tried opening up the jets from 1.6mm to 1.65mm and it got worse. Got a JAW AFR meter and tried again - found that the mixture was way too rich at full throttle. Tried 1.5 jets - better, but still too rich. Went through 1.4mm to 1.3mm - full throttle is now near perfect, at around 12 or 13 AFR. Throttle-off over-run is about 17 or 18, which is also what I want. The plugs are a nice mid-brown colour after a good run.

My only remaining issue is mid-throttle (which is used most of the time!) where it is still too rich - ideally I'd like the 'perfect mixture' of 14.7 while cruising along, but I can only manage 12.5 - 13.5. I have fixed needles, so sorting that out is a PITA. It's still WAY better than I could ever manage with the old down-draft DGV Weber!

So, after all that rambling, I concur with all the others who think your main jet is too large.

[Edited on 18/1/09 by David Jenkins]

What fuel pump are you using?

190's are what boggs put in. I think they were set up on a bench with no filter. i didnt have them done so its arkward to send them back with no proof etc.

It has never ran well since i built the car. Its definatley fueling. The plugs are nice and black.

I have rewired and checked the whole ignition system. When using maps that have came from peoples cars with virtually the same set up it still has this problem so im convinced its the carbs.

The slides move nicely and the diaphragms are sealed.

Ideally i dont want to spend alot more money on it if i can help it unless its to a place to sort it on a dyno. I have some 130 jets and a set of .5 drills so ill try them and see what happens.

David i have no boss etc to bolt a sensor in so unless i can clamp it in the end pipe. If i cant sort it without il get one welded in and go from there.

Anying me more is the fact that its a nice day again and i could be out in it!!!!

Thanks lads ill work through the suggestions this morning.

Carb'd R6 pump btw.

Dan,

Here's the one I welded in:



And here it is with the sensor in place (it doesn't normally live there):



I bought the boss off Nick Skidmore - you could ask if he's got any left...

Shout if you do fit one - I can bring my JAW unit over to you and we can try it out.

have u balanced the carbs?
is there an air leak in the inlet system?
are the float bowl at the correct angle?

have u balanced the carbs?
is there an air leak in the inlet system?
are the float bowls at the correct angle?

What model zx9r carbs do you have ?
I have zx9r / E carbs on a 2.1 pinto
tha main jets are drilled to 1.7mm
the air screws are one turn out
the main needles have two washers under the heads
and boggs blocked a air hole in the carbs that are in line with the main needles that was to stop the fuel /air mix going week at high revs

thats how mine is by Bogg Brothers
this may help you to get in the ball park
Jacko
ps have you had the carbs balanced?

These are zx9r /E carbs

carbs on manifold

The carbs are zx9rb's.

Right. I have changed the needles and slides for ones from the other carbs i have. The needles are slightly longer.

It is hell of alot better but still bogging down at 3/4 to WOT when u make it pull below 3.5k. If you back off it will pull over that then go like stink. Its still way overfuelling and spitting back through the carbs. The air filter is soaked and 24 miles to 2/3rds of a tank!!

Havent balanced the carbs. gonna get a thing and do it. The slides sit level.

quote:

---

Originally posted by Danozeman
Havent balanced the carbs. gonna get a thing and do it. The slides sit level.

---

will do that tomorrow. and see how it goes then.

190's seem a bit big, mine is still a bit rich on 170's, same setup but zxr750 carbs.

But mine did the same sort of thing before I blocked off the air correction jets as has already been mentioned.

It also may be worth checking the choke mechanism is closing correctly, I think on those carbs it is an auxillary jet that lets in extra fuel.
Paul.