| Author |
Message |
Paul Newman (Newman)
Member
Username: Newman
Post Number: 477
Registered: 12-2001
| | Posted on Sunday, September 15, 2002 - 3:20 pm: | |
Increase the pump jets a size or 2 up from stock. This will 'cover up' a stumble. I would leave the idle mixtures alone but might also mess with the main jets. Im running 140's and may go to 150's in the spring. Messing with the mains wont fix your stumble but give more power. |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 393
Registered: 11-2001
| | Posted on Sunday, September 15, 2002 - 2:21 pm: | |
Bill
My smog system is entirely removed, so no pumps, no injection, not even a thermal reactor at this time. Anyway, good advise to break in the engine for a while. I only have about 400 miles on it now and I really should let 1000 miles go by, check the valves, tighten the head nuts again, and check the timing before I worry too much about the stumbling tendency. |
Bill Sebestyen (Bill308)
Member
Username: Bill308
Post Number: 342
Registered: 5-2001
| | Posted on Sunday, September 15, 2002 - 12:27 pm: | |
Mitchell,
I want to correct a statement in my last post. The air pump introduces air upstream of the gas sampling ports so this will indeed affect air/fuel readings taken at the gas sampling ports. To get true air/fuel ratios at the gas sampling ports, you would need to disable the air pump system, if fitted. |
Bill Sebestyen (Bill308)
Member
Username: Bill308
Post Number: 341
Registered: 5-2001
| | Posted on Sunday, September 15, 2002 - 11:49 am: | |
Mitchell,
I understand your reluctance to further enrichen the mixture.
Do you have cats and an air pump fitted? If so, this will negate any air/fuel readings taken at the tail pipe. The gas sampling ports on the exhaust manifold runners will give a true reading though.
It's been my experience that if ignition and cam timeing are correct, bogging and stumbling during acceleration are often traceable to a lean condition. What happens when suddenly opening the carbs is significant reduction in air velocity at the carbs, causing fuel metering problems. The accelerator pumps are meant to supply extra fuel during this critical period of low vacuum. Some carburators, like Hollys, have both accelerator pump and power valve systems. The acclerator pump provides extra fuel short term, when the carbs are suddenly opened, and the power valve circuit provides a longer duration enrichment based upon vacuum. The DCNF carbs don't have a power valve function, so the only short enrichment is provided by the acclerator pump. The only way I can see to adjust this mechanism is to change the pump jets, modify the discharge hole, or change the accelerator pump cam. It may be that your engine wants the accelerator pump discharge delivered over a longer period of time.
The other thing is I've had some engine rebuilds take 1500 miles to fully break-in and really feel good. It might be wise to get some more miles on the car and change the plugs before doing the final, fine tuning. |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 392
Registered: 11-2001
| | Posted on Sunday, September 15, 2002 - 10:58 am: | |
Bill
I am reluctant to richen the mixture anymore that what I have now. The car is already "smelly" and enough soot is deposited on the rear trunk paint each time I drive it that ... (IMHO) it is rich enough. I will try the other suggestions and see where I am. I might be able to get a HC/CO meter from a fellow Fchat member to get a reading on how rich I am really running. |
Hans E. Hansen (4re_gt4)
Junior Member
Username: 4re_gt4
Post Number: 175
Registered: 4-2002
| | Posted on Saturday, September 14, 2002 - 4:15 pm: | |
Mine will bog if I give it too much throttle too soon. i.e. - I can't "jump" on it, but a fairly quick press of the throttle is OK. I just figure that it is an artifact of large carbs on a small engine. I'm usually quite gentle in 1st gear anyway. |
Bill Sebestyen (Bill308)
Member
Username: Bill308
Post Number: 340
Registered: 5-2001
| | Posted on Saturday, September 14, 2002 - 11:48 am: | |
Mitchell,
I think what you've done to date is correct. I think the next step with your timing is to confirm the advance mechanism is operating properly. To do this, I would observe the advance on the flywheel with a timing light. Confirim you are at 7 BTDC at idle and see where you are at 5000 rpm. Check that the advance is smooth for each distributor while slowly accelerating the engine from idle to 5000 rpm and back to idle. If all is correct, I would then move on to the carbs.
For the discription you are describing, a stumble during accelleration, I can think of a couple of things to try, but one at a time.
1. Enrichen your mixture adjustments 1/4 to 1/2 turn and test.
2. Replace your idle jets with the next larger ones and test. Try 1 again.
3. I'm not sure if anything can be done with the accelerator pump system, but you might want to investigate this. |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 386
Registered: 11-2001
| | Posted on Saturday, September 14, 2002 - 11:10 am: | |
I am fairly confident in the conversion, but I do not have any Sun machine to really dial it in.
What I did was to convert it, install the distributors, retard it all the way, then set the flywheel at 7 degrees BTDC, then advance it manually until there is a spark at the coil to ground. Repeat for the other distributor and then check the timing under running condition and adjust finally for both distributors timing to be at 7 BTDC.
That is the extend of what I can do at home without more sophisticated machines.
In this configuration, both distributors are master of their respective banks and are not related in anyway.
Right now, if I gradually increase the gas pedal, the car will take off fine. If I jump on it from a dead stop, it will stumble. I guess I will not win any drag race anytime soon (not that I would engage in such antics).
Assuming it is in the carbs, what would you look for? Accelerator pumps seem to work fine (it dumps gas down the throats, so ... it is fine). I will admit that I do not understand the progression circuit very well. |
billy bob (Fatbillybob)
New member
Username: Fatbillybob
Post Number: 46
Registered: 8-2002
| | Posted on Saturday, September 14, 2002 - 12:37 am: | |
If the crane is set up right it is probably in the carbs. One of the nice things I always liked about my carb 308 was that cool jump I would get from a dead stop. It never really bogged. There is a trick to it with clutch and acelerator too. I have not played with the 308 electronic conversion since before crane was allison xr700. I do remember however that the optical triggers and optical wheel had to be set up perfectly on the SUN distributor machine. Some people do other tricks to set these up but I found that the Sun machine really made a difference. You could totally dial in to the last degree the one distributor as the master and then just use one as a slave. Are you confident in the conversion? |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 385
Registered: 11-2001
| | Posted on Friday, September 13, 2002 - 11:39 pm: | |
For those who have converted from carbs to Crane ignition. Do you have a stumble on hard acceleration (from stop) and how did you solve it?
I now have 3.5 turns out from stop on all the idle screws and the popping is all gone (happy with that) but still have that stumble during hard acceleration from a dead stop. I am thinking it may be the progression circuit of the carbs and not the ignition system. What do you think? |