Fixed the TR7...but it runs badly Ideas?
Posted: 09 Jun 2016 17:39
by bonnietiler
Had a great day on my Son's TR7.. Fixed the headlight flashers...fixed the headlights..got the car to start and it starts instantly...but...
Although It revs off the clock in neutral sat on the drive..it's only Ok in first, it definitely seems to slow a little as you reach 4000rpm..this gets worse and prolonged in every gear.
I took the car out and test drove it..if you pull the choke though the problem is cured..so either the mixture has miraculously changed or it just isn't getting enough fuel. There is excellent flow from the pump...any ideas,he is bringing it round on Friday (Tomorrow) for me to perform some alchemy on!
Cheers
Bonnietiler
Re: Fixed the TR7...but it runs badly Ideas?
Posted: 09 Jun 2016 22:17
by FI Spyder
Vacuum leak in intake causing it to run lean. This results in high rpm in neutral, better with choke on as this artificially richens mixture. Cause; missing/leaking hoses, carb mounts separated at rubber.
Re: Fixed the TR7...but it runs badly Ideas?
Posted: 10 Jun 2016 02:46
by Hasbeen
I have never found revving a 7 is much use. I did some testing a few years ago. I had always felt revving past 4000 RPM was a waste of time but even I was surprised by the results.
I did rolling acceleration tests in 3Rd & 4Th gears. I timed the period to accelerate from 40 MPH to 50, & from 50 to 60. Using MPH rather than RPM meant the speeds & the air resistance was the same.
I don't remember the actual times & can't find the notes, but it accelerated quickest from 40 to 50 in 4Th, & the slowest was from 50 to 60 in 3Rd.
I then tested 45 to 55 in top, & it was the second quickest acceleration of my test. I have rarely revved past 4000 since, unless I an holding a gear as I approach a corner.
With your tuning problem, Spyder may have hit the answer, however if not it is probably simple tuning. It is obviously running lean, [is it over heating from this?]. Applying choke in an SU is exactly the same as richening the mixture with the mixture nut. Do the normal mixture adjustment & see what happens.
Has the thing received any performance "improvements"? Just fitting good easy flow air filters make a fair improvement in power, but will not work well by themselves. We have found it takes a 3 stage richer needle to correct the mixture when such filters are fitted.
Add in an extractor exhaust & it will need even richer mid range needles to fix the mixture. In either case you can't get the mixture back to correct, without changing the needles. It can be got to running almost OK, but not well.
Do have fun, won't you.
Hasbeen