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A15 problem
Posted: Tue Jan 06, 2015 9:50 pm
by 1200 Koozer
Hey guys.
Iv just started my freshly rebuilt A15 set my ignition timing to 7deg before tdc check all my valve lash gaps. Its idlling good considering how hot the cam is but it seems that when i start to drive its sputters pops and farts and doesnt gain speed. I have a standard a15 hitachi carb. My ideas on what it might be are
1. Timing mark on crank pulley is wrong and therefore timing and advance is out. Are a12 and a15 crank pulleys same.
2. Carb is soo out of tune. How many turns out from closed gives a near enough baseline tune.
3. Carb jets are to small to compensate for hotter cam.
Any ideas guys
Re: A15 problem
Posted: Tue Jan 06, 2015 10:37 pm
by classicdat
1200 Koozer wrote:
1. Timing mark on crank pulley is wrong and therefore timing and advance is out. Are a12 and a15 crank pulleys same.
Yes the marks should be the same as the timing covers interchange. Do you have the vacuum advance hooked up?
2. Carb is soo out of tune. How many turns out from closed gives a near enough baseline tune?
The mixture screw will probably be near enough if it is idling, maybe the accelerator pump is not working, check you get a jet of fuel in the carb throat when you open the throttle
3. Carb jets are to small to compensate for hotter cam.
Yes jetting may not suit. Do you have any experience with this carb on another motor, is it a fault free carb or a mystery carb?
This probably isn't the problem as down drafts are fairly forgiving, but my cam was too wild for my SUs and had too much overlap causing pulsing in the manifold and robbed me of low down power.
Any ideas guys
http://www.nzdatsun.com/forums/posting. ... =7&p=75925#
Re: A15 problem
Posted: Tue Jan 06, 2015 10:52 pm
by mint16
Timing should be set in accordance to cam specs.
Mixture tune for idle should be set accurately, with correct idle speed and timing. How reliable is the carb?
Is the cam to suit a downdraught carb?
Re: A15 problem
Posted: Tue Jan 06, 2015 11:34 pm
by 1200 Koozer
classicdat wrote:1200 Koozer wrote:
1. Timing mark on crank pulley is wrong and therefore timing and advance is out. Are a12 and a15 crank pulleys same.
Yes the marks should be the same as the timing covers interchange. Do you have the vacuum advance hooked up?
2. Carb is soo out of tune. How many turns out from closed gives a near enough baseline tune?
The mixture screw will probably be near enough if it is idling, maybe the accelerator pump is not working, check you get a jet of fuel in the carb throat when you open the throttle
3. Carb jets are to small to compensate for hotter cam.
Yes jetting may not suit. Do you have any experience with this carb on another motor, is it a fault free carb or a mystery carb?
This probably isn't the problem as down drafts are fairly forgiving, but my cam was too wild for my SUs and had too much overlap causing pulsing in the manifold and robbed me of low down power.
Any ideas guys
http://www.nzdatsun.com/forums/posting. ... =7&p=75925#
Re: A15 problem
Posted: Tue Jan 06, 2015 11:35 pm
by 1200 Koozer
classicdat wrote:1200 Koozer wrote:
1. Timing mark on crank pulley is wrong and therefore timing and advance is out. Are a12 and a15 crank pulleys same.
Yes the marks should be the same as the timing covers interchange. Do you have the vacuum advance hooked up?
yes all hooked up fine how do i test this? Possibly a leak throwing me out maybe ?
2. Carb is soo out of tune. How many turns out from closed gives a near enough baseline tune?
The mixture screw will probably be near enough if it is idling, maybe the accelerator pump is not working, check you get a jet of fuel in the carb throat when you open the throttle
Good thought i will check in morning.
3. Carb jets are to small to compensate for hotter cam.
Yes jetting may not suit. Do you have any experience with this carb on another motor, is it a fault free carb or a mystery carb?
This probably isn't the problem as down drafts are fairly forgiving, but my cam was too wild for my SUs and had too much overlap causing pulsing in the manifold and robbed me of low down power.
unfortunately i have brought this carb assuming it is working i cleaned it up and had a look before installing and everything seems good mind you im no carb expert. I also bypassed the anti dieseling solenoid as it was missing connection tabs. I know the a15 hitachi has a vacuum controled secondary barrel how do i test this.
Cheers for the help
Any ideas guys
http://www.nzdatsun.com/forums/posting. ... =7&p=75925#
Re: A15 problem
Posted: Tue Jan 06, 2015 11:40 pm
by 1200 Koozer
mint16 wrote:Timing should be set in accordance to cam specs.
Mixture tune for idle should be set accurately, with correct idle speed and timing. How reliable is the carb?
Is the cam to suit a downdraught carb?
i will check cam specs tommorrow. Unsure on carb it could do with a rebuild. Thanks for the help mate
Re: A15 problem
Posted: Tue Jan 06, 2015 11:49 pm
by 1200 Koozer
New possibility i found below. But i would have thought the new electric pump i put in would be fine will test tomorrow
Low fuel pressure often has this symptom: Engine idles fine, but when you "give it the foot" it runs poorly, backfires or runs slows down. High fuel pressure can cause poor fuel economy or flooding (raw fuel running down throttles). Perform the fuel pump pressure test to be sure the fuel pump is working correctly.
Re: A15 problem
Posted: Wed Jan 07, 2015 10:14 am
by classicdat
Low fuel pressure would result in lowering the fuel level in the fuel bowl, to check confirm if this changes. Have you set the float level?
When you say you have bypassed the Anti-Dieseling what do you mean? This is an important item and is used to shut off the low speed circuit of the carb.
Have you confirmed the operation of the accelerator pump?
Does your car back fire?
Re: A15 problem
Posted: Wed Jan 07, 2015 11:20 am
by beaver
classicdat wrote:
When you say you have bypassed the Anti-Dieseling what do you mean? This is an important item and is used to shut off the low speed circuit of the carb.
Could you expand on this? I was of the undersading that it gets it signal on/off when the ignition is switched on/off and it just stops dieseling? Mine isnt operatinoal as the wiring has been ripped out of the valve, but if it plays another role (other than just cutting the fuel when the car is off) then Ill get another one.
Cheers
Re: A15 problem
Posted: Wed Jan 07, 2015 1:19 pm
by classicdat
You are correct, it stops preignition, by switching off the low speed circuit. If you have prevented the spring from isolating this circuit and running on isn't an issue then no problems. In my limited and aging understanding
