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s u h4 needles

bodyshell2

Freshman Member
Offline
Hi I have build a 1340 cc engine with a 649 cam i am running a MED fast road / race head 36mm 30mm valves sizes compression ratio is 10.5 to 1 the carbs are twin H4 1"1/2 SU's can anyone give me a jet set up jet to start me off . Unfortunately there are no dyno,s available near my location and will have to do it the trial and error method .

Many Thanks
 

Jerry

Luke Skywalker
Gold
Offline
I have a 1380 with hot cam and similar compression. I have tested about 12 different needles and none are perfect. I think you will have to buy some and then start testing. I found too much fuel at low throttle, but good at high throttle. In all my testing, I could not get the excess fuel at low throttle to go away. By the way, my engine dyno was 95hp at the wheels so upper range is very good. I have a fuel/air meter to fine tune the car. Very necessary in my opinion. In general the 1.5 inch are too much carb so start with a normal or lean needle and experiment from there.
Jerry
 

Joe Schlosser

Jedi Trainee
Silver
Offline
I have a plus 40 overbore 1275 with your cam and am about 9.5:1. I am currently running AH2 needles on HS2 carbs. On a hot shutoff they look pretty good. I agree with Jerry that HS4 is over carbed.
I ran HS4 with full race everything (112 at the wheels) but not needed on a street motor.
Suggest you drop back to HS2 carbs.
 

Jerry

Luke Skywalker
Gold
Offline
I did try the mikuni carbs on my car. Still too much fuel at low throttle. But the car screamed like a Harley at high RPM!
 

Jerry

Luke Skywalker
Gold
Offline
I have a 286 cam, too hot for street use. So I got the 95HP at 5500 rpm. THat was the number I was shooting for. I bought the 1.5 carb set because I did not have any carbs. So I made them work. But the air/fuel ratio is key. At low Rpm, I watch the meter and if below 11, I know the engine is drowning in gas, and does not accelerate. But if you press the pedal slowly, it will catch up quicker and then take off like a rocket. I think these carbs give you a little more at high rpm at the sacrifice of low. If I did this engine over:
1. less carbs,
2. less cam
3 end ratio stock instead of 2.9 ( I only notice this issue in the mountains. Freeway it is great.)

Maybe smaller exhaust, the large bore is quite noisy. In any case it is a fun car to drive. In the mountains, my Healey is easier because I don't have to shift on the hills. But the mini would probably be more like that with the original end ratio.

Jerry
 
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