DarrenW
|
| posted on 20/8/05 at 11:31 PM |
|
|
Carb Blowback
As posted in Locost related section i have just got my engine running. Iamgetting blowback thro the carb, wife was a little scared when she saw a
quick flame blowback.!!!!!!!
Engine bottom end is std 2.0 pinto, 90K miles. Head started life as injected version, mildly ported as per Uncle Hammil advice, new guides / seals,
FR32 cam (fast road 285 deg Kent), 40" skim. Carb is 38DGAS allegedly jetted for RS2000 (just had to replace perished accelerator pump diaphragm
- dont know condition of power valve). Ignition is brand new electronic (dizzy and amp).
Is blowback just the result of needing to tune timing (with strobe) and fuelling setup???? I have only static tuned so far, and that will be only
roughly at best cos ive never done this before. To be honest i dont know what advance to set to for this head mod / bottom end combo (10 deg or
14deg???) or how to read the pulley correctly.
One pther point - vacuum take off from inlet manifld is blanked off (ie dizzy vac advance not connected) nd i havent got cooling connected yet so have
only been able to fire up for a few secs at a time.
I dont understand how to align rotor arm to dizzy notch - do you align leading edge of rotor arm to notch or centre of rotor arm to notch????
Thanks for your great help again,
Darren.
|
|
|
|
|
JoelP
|
| posted on 20/8/05 at 11:37 PM |
|
|
im (fairly!) sure you can loosen the distributor and twist it whilst its running, to see what position is best. never done it myself though.
mine has no vacuum advance plumbed, the fella at the rolling road thought it was better this way, but mine is a diferent setup to yours so it might
not hold true.
|
|
|
mookaloid
|
| posted on 21/8/05 at 07:25 AM |
|
|
You can adjust your dizzy with the engine running. Just make sure it doesn't pink when you get it on the road.
A rolling road session will sort it out for you - £50 well spent in my opinion.
With a single carb, there is no reason to disconnect the vacuum advance It improves the timing at lower revs and makes it easier to start. The only
reason the non vac dizzys are used is when you have twin 40's etc and there is no easy way to get a suitable take off point.
the rotor arm notch is in the centre of the contact and this should align with the notch in the dizzy body as a rough starting point when no. 1
cylinder is on it's firing stroke - the Haynes manual tells you how.
Actual timing can vary from engine to engine so to say it should be 10 or 14 or 12 degress is probably not the way forward (although 12 is probably a
fair starting setting) . The rolling road man should be able to sort out which is best for your engine after seeing it perform on the rollers.
Hope this helps
Cheers
Mark
|
|
|
rusty nuts
|
| posted on 21/8/05 at 10:32 AM |
|
|
Would recommend that you get cooling system sorted before worrying about ignition timing ,carb etc . Once you can run engine for longer then you can
set timing , would have thought 10 to 14 degrees at idle should be O.K. until you get to rolling road . Is the 38DGAS a manual choke carb? could be
spitting back due to weak mixture because of not enough choke when cold , again can be adjusted when engine is warm .
|
|
|
britishtrident
|
| posted on 21/8/05 at 10:58 AM |
|
|
check the Firing order
|
|
|
Surrey Dave
|
| posted on 21/8/05 at 11:32 AM |
|
|
Could indicate weak mixture........
|
|
|
DarrenW
|
| posted on 22/8/05 at 10:05 AM |
|
|
It looks like the solution has now been identified;
1. Cos i havent got cooling system plumbed in and carb doesnt have any choke, i cant get it up to temperature so it hasnt had chance to settle down.
This should be sorted by this weekend.
2. I have static timed everything up spot on apart from the dizzy. Ive aligned the leading edge of rotor arm to the dizzy notch instead of the rotor
arm centre point - again easy fixed.
After i get all this sorted ill turn attention to mixture later.
I didnt think there was much wrong as it starts so easily from cold without choke after such a basic set up.
Many thanks for all of your help - inc those who chose to ring for a chat instead of posting.
It still sounds very sweet. I have a permanent grin at the moment. I have excess inspiration now as well so dont think it will take me long to
complete the car.
|
|
|
.jpg)
