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Flat spot with 107 jet
http://www.international2cvfriends.com/forum/viewtopic.php?f=7&t=5565		 Page 1 of 2
Author:  adam_d [ February 23rd, 2015, 9:48 pm ]
Post subject:  Flat spot with 107 jet
On my last order of bits, I ordered a 107 jet to try and help smoothen the second choke transition a bit (it is stamped 105, but I guess may have been drilled). After fitting, the car suddenly gained a massive flat spot on the first choke, just after pulling away. You could drive through it and the car would pick up again, but it made pulling on to roundabouts or out of junctions a bit interesting. It also stuttered a bit if you were going uphill at this point.

The 102 I took out was a bit chewed up (and I might have lost it :oops:), but I have borrowed another 102 temporarily to try it and the car is back to normal. The jet is the only thing I have changed, and went straight from the packet into the carb. Floats are at 18mm.

Is there something else I should have done when I put the new jet in? There don't seem to be any issues with the car, just this one caused by me changing the jet. It would be good if I could get this new jet working, as the 102 in there now is just borrowed.

Thanks.
Author:  ken [ February 23rd, 2015, 10:46 pm ]
Post subject:  Re: Flat spot with 107 jet
Sounds as though there may have been some debris dislodged when fitting the first jet, which restricted the amount of fuel it could pass.
Did you clean the interior of the float bowls with an air line whilst the lid was off?
Author:  Sean [ February 24th, 2015, 9:15 am ]
Post subject:  Re: Flat spot with 107 jet
check the 107 is actually a 107 sounds strange but i had exactly the same thing and the 107 was not any larger than the 102 it had replaced.
Author:  adam_d [ February 24th, 2015, 7:36 pm ]
Post subject:  Re: Flat spot with 107 jet
I did quickly blow the carb out as there were a couple of bits of muck in the bottom, and I blew out the other jets while I was there.

I won't get chance to look at it again until tomorrow, so I'll compare the jet sizes then, clean it all out again and post back.

Thanks.

Edit: Had a proper look at it tonight, with the car properly cold it wasn't much better with the 102 in. Tried the 107 back in with it warm and it's still a little flat, but much better warmed up.

I do think I have found the cause though, not sure how I missed it the first time. When I was putting the 107 in this time, there's a big split in the carb top gasket on the primary choke side, with a little bit missing. I haven't got one to hand to try but I think that's probably my issue.
Author:  adam_d [ February 28th, 2015, 6:44 pm ]
Post subject:  Re: Flat spot with 107 jet
I've put a new carb gasket in and it's the same now. When it's cold theres a massive flat spot, when it warms up it's a lot better but it seems a bit down on power overall.

This started when I changed the jet originally, it's the perfect reasoning for "if it ain't broke..." :lol:
Author:  ken [ February 28th, 2015, 8:05 pm ]
Post subject:  Re: Flat spot with 107 jet
Adam,
the jets I sent for your friend's Ami did what they're intended to do, so rather than 'if it isn't broken...', shouldn't the motto be 'if you're going to fix it, do it right'? ;)

If you post that replacement jet to me, I can check and return it, as long as you enclose an SAE.


adam_d wrote:
I've put a new carb gasket in and it's the same now. When it's cold theres a massive flat spot, when it warms up it's a lot better but it seems a bit down on power overall.

This started when I changed the jet originally, it's the perfect reasoning for "if it ain't broke..." :lol:
Author:  Sean [ March 1st, 2015, 5:04 pm ]
Post subject:  Re: Flat spot with 107 jet
Adam sounds like there is a problem elswhere with the car - as with all things carb you have to make sure the timing is spot on, the tappets are done there is no leaks anywhere in the inlet side of things

Then you should check that the 2nd choke butterfly is closing properly Corrosion and fiddling can have it moved off its seat allowing "false air" and a flatspot

Then you will probably have to have a re set of the idle speed and the idle/ bypass/co2 jet

Tuning a carburretor car to get the best out of it isnt a case of just substituting parts...sorry if its a grandmother / egg situation

>edit<
oh remember that a popped dust cver behind the points box can drag on the advance weights causng what feels like a flat spot - you can usually see the scuffs or if you set the timing with a strobe the timing mark stays stationery then suddenly jumps as you increase the revs.
Author:  adam_d [ March 2nd, 2015, 12:19 am ]
Post subject:  Re: Flat spot with 107 jet
ken wrote:
If you post that replacement jet to me, I can check and return it, as long as you enclose an SAE.


Thanks Ken, I will send you it if that's OK.

Sean wrote:
Tuning a carburretor car to get the best out of it isnt a case of just substituting parts...sorry if its a grandmother / egg situation


Thanks Sean, no not at all, I'm still fairly new to messing with carbs. I did a timing and tappets a couple of weeks back before I switched the jets and the car was OK after that. I'll check the second choke flap and the gaskets and block at the base, thanks.

It didn't seem anywhere near as bad today for some reason, much less noticeable when cold, but still there all the time. You notice most when pulling away or when on a hill in 2nd or 3rd, at low revs it's fine then it hits this flat spot, then suddenly picks up again.

Thanks for your help. :)
Author:  citroenboat [ March 2nd, 2015, 11:09 am ]
Post subject:  Re: Flat spot with 107 jet
Most recent(?!) probs I had turned out to be crud in the 'cleaned' carb. Application of lotsa petrol to the dismantled parts followed by compressed air sorted it. It was a frustratingly intermittent problem which suggested to me that it wasn't dirt in the carb as I always thought that was an 'on' or 'off' problem, wrong again.
Author:  adam_d [ March 26th, 2015, 9:22 pm ]
Post subject:  Re: Flat spot with 107 jet
Pleased to say this now seems to be sorted. :)

I haven't had a ton of spare time lately, so only managed to sort it properly. I took the carb off and found that the spacer was starting to crack and the bottom gasket was looking pretty tired, so replaced both of them.

While it was off, I had a go at it with the carb cleaner and compressed air wherever I could get them in. Let it sit with fresh petrol in for a while, blew everything out again, and reassembled with the 107 Ken kindly checked out for me.

After a bit of setup, it seems perfect. Runs well, and there is definitely improved pickup and smoothness with the 107 in. This is the first time I've done the idle mixture myself from scratch, it's currently at just about 4 turns out, does that sound about right?

Thanks for the help.
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