Blowback.....could this be MJ related?.
Moderators: JeffC, rdoherty, stieg, brentp
Hi Gents,
Firstly, thanks for your inputs, it's very much appreciated, and keeps me going (and interested to find the fault).....I can't wait to put that post up here that say....wayyyyyyyhheyyyyyy...it's fixed
Anyway, for now, we'll keep plugging away....
So, to comment on what has been said.....
Firstly Valve bounce / coil binding....This was one of my first suspicions...so I actually invested a load of cash ona a rather nice set of double valve springs from Newman cams......made no difference!....but nice to have anyway
The lifters were new over winter when I built the head, and I used the ones supplied with the piper Cam kit (which were the antipump followers)....So they should be fine...
The MJ rev limit is set at 7000rpm...tripple checked that one, assuming the rev limit is only set under the 'Additional configurable ouputs section under options tab???......
Have tried two coils now, and made no differnce....
As mentioned, I think a compression test is a very good idea, although car does work and feel fantastic right up to this point, so if there was a lack of compression, I would imagine I would feel it throughout the rev range...However, a simple test, and I'll try this.....
The rolling road was simply a shootout day for our Westfield club....the chaps running it were young lads, who were very knlodgeable about maping of ECU's and fuel injection, but really were not into carbs...plus time was very limited, as it was a quick run and then on to the next car....However, the AFm was also logged, and actually looked very good for a carb, up to the point of the standoff, where it shot up and measured lean (to be expected as there was effectively no fuel in cylinders 1 and 2).....
Have looked at plugs, and they look fine, and are very good quality ones.....
Air leaks - interesting, although I was of the understanding that this has more of an effect at closed throttle....When the butterflies are wide open, and air leak should not make too much difference as the air velocity is very high....However, I'm not discounting this, will try the WD40 test anyway....
Looks like I have a few things to go off and try...so watch this space, and thanks again for all your help thus far....
Paul.
Firstly, thanks for your inputs, it's very much appreciated, and keeps me going (and interested to find the fault).....I can't wait to put that post up here that say....wayyyyyyyhheyyyyyy...it's fixed
Anyway, for now, we'll keep plugging away....
So, to comment on what has been said.....
Firstly Valve bounce / coil binding....This was one of my first suspicions...so I actually invested a load of cash ona a rather nice set of double valve springs from Newman cams......made no difference!....but nice to have anyway
The lifters were new over winter when I built the head, and I used the ones supplied with the piper Cam kit (which were the antipump followers)....So they should be fine...
The MJ rev limit is set at 7000rpm...tripple checked that one, assuming the rev limit is only set under the 'Additional configurable ouputs section under options tab???......
Have tried two coils now, and made no differnce....
As mentioned, I think a compression test is a very good idea, although car does work and feel fantastic right up to this point, so if there was a lack of compression, I would imagine I would feel it throughout the rev range...However, a simple test, and I'll try this.....
The rolling road was simply a shootout day for our Westfield club....the chaps running it were young lads, who were very knlodgeable about maping of ECU's and fuel injection, but really were not into carbs...plus time was very limited, as it was a quick run and then on to the next car....However, the AFm was also logged, and actually looked very good for a carb, up to the point of the standoff, where it shot up and measured lean (to be expected as there was effectively no fuel in cylinders 1 and 2).....
Have looked at plugs, and they look fine, and are very good quality ones.....
Air leaks - interesting, although I was of the understanding that this has more of an effect at closed throttle....When the butterflies are wide open, and air leak should not make too much difference as the air velocity is very high....However, I'm not discounting this, will try the WD40 test anyway....
Looks like I have a few things to go off and try...so watch this space
, and thanks again for all your help thus far....Paul.
Update...........
I actually took a vid of the engine showing the problem........
What you are seeing is unburnt fuel / air mixture squirting backout from the carbs....however, as you will notice, it's both carbs, not just the first one....for some reason I did not notice this from being sat in the car.....
I can only assume there is some positive pressure on the cylinder when the inlet valve is opened.......I need to have a close look at my cam timing...just wondering if it has jumped a tooth?.........
http://s34.photobucket.com/albums/d102/ ... CF1479.flv
Cheers.
Paul.
What you are seeing is unburnt fuel / air mixture squirting backout from the carbs....however, as you will notice, it's both carbs, not just the first one....for some reason I did not notice this from being sat in the car.....
I can only assume there is some positive pressure on the cylinder when the inlet valve is opened.......I need to have a close look at my cam timing...just wondering if it has jumped a tooth?.........
http://s34.photobucket.com/albums/d102/ ... CF1479.flv
Cheers.
Paul.
-
capri_turbo
- Posts: 122
- Joined: Tue Jan 10, 2006 8:17 pm
- Location: North Yorkshire, UK
Thanks guys....
It is rather impressive, and if it happened at 6800rpm I'd be a happy man....Alas, at 5500rpm, it's not so good..........
I have tried moving the vernier on the cam pulley, but it made no difference.....however, someone has suggested that mabe my cam belt has jumped a tooth?.....I'm going to double check the cam timing at the weekend and make sure everything is as it should be
Thanks for sending the vid around, someones gotta know
Cheers.
Paul.
I have tried moving the vernier on the cam pulley, but it made no difference.....however, someone has suggested that mabe my cam belt has jumped a tooth?.....I'm going to double check the cam timing at the weekend and make sure everything is as it should be
Thanks for sending the vid around, someones gotta know
Cheers.
Paul.
When it hits approx 5500rpm it starts, and the car (and me)will be reluctant to rev much higher, the rev rate slows dramatically, and putting my foot to the floor only seems to aggrivate the engine into blowing more fuel back, and making in more nasty noises........After it has happen the engine runs a bit rough for a few seconds, but I'm guessing this is due to possibly a flooded cylinder or carb clearing it's self (quite a bit of fuel pools up in the carbs)........
Another thought I had.....How sensitive is MJ to plug gaps...I read somewhere that people were running with a 1.5mm gap, so I have just had a flash back of increasing my gap.....I'm not 100% sure my plugs were designed to be changed...they are NGK platinum or iridium cant remember which at the mo.....
Would too much gap cause problems like this?....Just a thought.
Another thought I had.....How sensitive is MJ to plug gaps...I read somewhere that people were running with a 1.5mm gap, so I have just had a flash back of increasing my gap.....I'm not 100% sure my plugs were designed to be changed...they are NGK platinum or iridium cant remember which at the mo.....
Would too much gap cause problems like this?....Just a thought.
-
capri_turbo
- Posts: 122
- Joined: Tue Jan 10, 2006 8:17 pm
- Location: North Yorkshire, UK
My mate has got back to me.
When he says agree with above, this refers to comments made by other Capri Laser Page forum members, which say cam timing.
well Colin, i wouldnt say expert... July 12 2007, 4:36 PM
but ive had a fair bit to do with em...
agree with above, cam timing, problem gets worse with more duration, mine does it a bit with a 285 profile but they get quite bad with 300 duration cams upwards..
if it was ignition timing you have the same but the stand off is allight (spit backs).
what engine? (does sound sweet) and cams is he using, it may be worth retarding the inlet cam a few degrees.
Also try...... July 12 2007, 4:38 PM
Going down a size or two on the choke size, it will cost a small amount of power, but at least he wont be throwing (expensive) petrol out the wrong end of the carbs.
Hope this helps you. FYI, when he says his does it too, he is running a 2 litre Pinto on twin DCOE's and has run all sorts of old skool fords over the years and I REALLY trust his judgement on such things.
When he says agree with above, this refers to comments made by other Capri Laser Page forum members, which say cam timing.
well Colin, i wouldnt say expert... July 12 2007, 4:36 PM
but ive had a fair bit to do with em...
agree with above, cam timing, problem gets worse with more duration, mine does it a bit with a 285 profile but they get quite bad with 300 duration cams upwards..
if it was ignition timing you have the same but the stand off is allight (spit backs).
what engine? (does sound sweet) and cams is he using, it may be worth retarding the inlet cam a few degrees.
Also try...... July 12 2007, 4:38 PM
Going down a size or two on the choke size, it will cost a small amount of power, but at least he wont be throwing (expensive) petrol out the wrong end of the carbs.
Hope this helps you. FYI, when he says his does it too, he is running a 2 litre Pinto on twin DCOE's and has run all sorts of old skool fords over the years and I REALLY trust his judgement on such things.
Thanks again for this.....more and more point to Cam timing...............
To answer his questions....
The engine is a 2ltr CVH, with a ported head, and a 280 duration cam kit from piper (which is specced to rev to 7k rpm although I'd be happy with 6.5k rpm)........
The carbs are 40's with 34mm chokes, which should!!! be fine, and are on the small size for this engine........
Will try Cam timing first............Cheers...Paul.
To answer his questions....
The engine is a 2ltr CVH, with a ported head, and a 280 duration cam kit from piper (which is specced to rev to 7k rpm although I'd be happy with 6.5k rpm)........
The carbs are 40's with 34mm chokes, which should!!! be fine, and are on the small size for this engine........
Will try Cam timing first............Cheers...Paul.
-
molecular bob
- Posts: 21
- Joined: Fri Mar 02, 2007 7:34 am
- Location: Sheffield UK
spit back
Do you have any other ram pipes that you could try? Spit back on Webers can be a resonance effect, which you can move around the rev range with longer or shorter ram tubes. I think shorter should move it further up the range, possibly to a point above your rev limit, but may alter your power curve.
My crossflow does it a bit without the filters on but with the filters in place (K&N metal plate style) it goes away, which may be due to pressure wave reflections from the front plate of the filter.
My crossflow does it a bit without the filters on but with the filters in place (K&N metal plate style) it goes away, which may be due to pressure wave reflections from the front plate of the filter.
In the lab or in the car
Update.....
Alas, retimed the cam on the weekend, and it was pretty close to what it should be, anyway, it didn't help....
So, back to the drawing board for me......will try the different ram pipe length to see if that moves said problem around......even if I could find something that changes where it is, that would be a huge help.....
Cheers guys.
Paul.
Alas, retimed the cam on the weekend, and it was pretty close to what it should be, anyway, it didn't help....
So, back to the drawing board for me......will try the different ram pipe length to see if that moves said problem around......even if I could find something that changes where it is, that would be a huge help.....
Cheers guys.
Paul.
-
molecular bob
- Posts: 21
- Joined: Fri Mar 02, 2007 7:34 am
- Location: Sheffield UK
spiting back
Where are you located? If you are midlands based, a trip to Northampton Motorsport is to be recomended. They are happy with carbs and also megajolt mapping on their rollers, I think they used to be around £90 an hour plus parts if you need to get new jets or chokes (not sure if they carry stock of chokes).
In the lab or in the car