Author Topic: 1978 F 750 Starts with help Can't keep it running (Read 2400 times)

Jnel · « **on:** November 30, 2018, 08:30:58 am »

I installed a new set of aftermarket coils. I have a question about the Leads coming from the points. Do they go to the positive side or the negative side of the coil?

I figured that the positive side of the coil should be the side that gets 12 V all the time.

I'm not getting any Spark.

Could I have these hooked up wrong?

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bryanj · « **Reply #1 on:** November 30, 2018, 08:50:17 am »

Black wires go to white and black from loom yellow and blue wires go to similar wires to points

bryanj · « **Reply #2 on:** November 30, 2018, 09:25:59 am »

Opposite to that, +ve is power in -ve is to points

Jnel · « **Reply #3 on:** November 30, 2018, 10:02:47 am »

Ok cool. Thank you. Let me give that a go and see what happens.

I appreciate your time with this.

Jnel

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Jnel · « **Reply #4 on:** November 30, 2018, 12:52:17 pm »

Well I had No luck with the new coils so I put the old coils back in. Hook them up the way they were supposed to be which is kind of idiot proof. I ended up getting spark out of the number one and number 4 cylinders but I got nothing not a 2 and 3. Have a look at the points in their definitely spark and on the 2 and 3 side. So I guess I'm gonna try and cut a little bit off the a spark plug wire on 2 and 3 may be quarter of a inch put the cap back on and try that.

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Jnel · « **Reply #5 on:** December 01, 2018, 10:09:12 am »

It finally ran.http://cloud.tapatalk.com/s/5c02ce494405e/InShot_20181201_105433330.mp4

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Jnel · « **Reply #6 on:** December 01, 2018, 12:12:53 pm »

Ok... so I got it to fire. If you can see the video, you'll note that it will only run for a short time. I had to give it a short blast of starting fluid. I know... this is not the best thing to do, but it got me to the point where I know that it will run.

So back to the issue.... The fact that it dies out on me seems to indicate that it's not getting fuel. Here are some facts about the situation.

*** I cleaned and rebuilt the carbs. New everything inside.
*** I did not replace the pump because it looked to be in good shape.
*** I know I have an issue with right side carb and I think its the float because it dumps fuel out of the overflow hose.
*** The bike has pods on it and I went up one size. I know I'm going to have to mess with that.

I was thinking that the fuel pump is a possible problem. Is there an "on bike" test for this pump?

I'm getting close now and I'm starting to get a little bit excited.

Thanks,

Jnel

Jnel · « **Reply #7 on:** December 01, 2018, 12:18:41 pm »

Oh.. BTW... The reason I was able to get it running was because I had set the points gap wrong. Fixed that and I was good to go.

Don R · « **Reply #8 on:** December 01, 2018, 02:07:27 pm »

Crank the throttle while looking in the carbs, you should see a squirt of fuel. The tubes between the carbs contain small fuel restrictors don't lose those if you get new hose. Check the plugs, wet or dry? Fix #4 and recheck float levels again.

Jnel · « **Reply #9 on:** December 01, 2018, 02:42:19 pm »

Thank you Don. I'll give that a try. I'm going to drop the bowls on all of them tomorrow and see what I can see..

Appreciate the kick back!

John

TwoTired · « **Reply #10 on:** December 03, 2018, 09:23:23 am »

If it doesn't want to idle, it is probably the pilot jets plugged. These are press in for the PD carbs, but still must be yanked out to clean them properly. Lot's of posts about cleaning these and them being overlooked. There are many posts about cleaning carbs three times before they actually got clean enough to operate well.

A fuel pump issue would be related to throttle opening under acceleration. That's why it's called an accelerator pump.
You might still have an issue with this. But, it won't stop the engine from running.

Cheers,

Jnel · « **Reply #11 on:** December 03, 2018, 11:07:58 pm »

Thank you Too Tired. I'll have a look at the pilot jets. I've heard they can be a pain to get out. Tomorrow if I can get to it, I'm going to clear tube the carbs and see how I'm doing there. I'll read up on the pilot jet cleaning.The accelerator pump makes perfect sense to me now. Maybe some day soon I'll actually get to accelerate.

Thanks all for the help. Much appreciated.

Jnel

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Bankerdanny · « **Reply #12 on:** December 04, 2018, 09:02:27 am »

(a) Are you operating the choke properly? Without choke it will fire on starter fluid, but won't stay running (b) if it fires on fluid but won't stay running (and you are using the choke correctly) then you have a fueling issue and the first place to start is the idle jet.

TwoTired · « **Reply #13 on:** December 04, 2018, 09:18:39 am »

Good point about the choke.
These are adjustable at the cable. I had one that couldn't be applied fully due to faulty adjustment. Cold starting was problematic. Something else to examine. If you pull the knob out all the way, do the choke plates fully close?

After it starts, you gradually push the knob in until the motor is warm enough to run without choke.

Cheers,

Jnel · « **Reply #14 on:** December 05, 2018, 09:57:05 am »

Good afternoon gentlemen.

I remove the idle jets from all 4 carburetors they're in good shape andI replaced them turning each one out 1 and a 1/2 turns.

I adjusted the floats in all 4 carburetors. I use the clear to method and they're all reasonably good.

When I put them back together the number for carburetor did not overflow. So this was a good sign.

With regards to the choke situation, it is fully closed when I apply the choke. Have a good strong battery and it turns over really well.

I forgot who it was who said this... but somebody said if I give the throttle a couple of quick snaps that I should see fuel coming out of the accelerator pump nozzle. This is not happening. I engage the starter and gave the throttle a few more pumps and still nothing out of the accelerator pump nozzle. These carburetors are bone dry during the starting process, So I think I have a Fuel issue. I can't even smell fuel.

Starting fluid does make it fire but and only runs for just a few seconds. After the starting fluid Burns off ... Nothing!

There is definitely Fuel in the bowls, But it's not making it's way up to the upper part of the carburetor. Frustrating!

Thanks for all the comments. Its helping.

Regards,
Jnel

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Bankerdanny · « **Reply #15 on:** December 05, 2018, 10:57:36 am »

"I remove the idle jets from all 4 carburetors they're in good shape and I replaced them turning each one out 1 and a 1/2 turns."

~~What you are describing is the idle air screw, not the jet. The idle jet is located next to the main jet on the bottom of the carb body.~~

Sorry, I assumed the PD carbs on your bike was similar to the version on my '77 550k, but after looking at the shop manual I see that I am incorrect.

That said, if you remove the pilot screw and spray carb cleaner into the hole through the red tube that comes with the can, do you see any spray into the carb body? It sure sounds like the hole that the fuel goes through, with the screw acting as a restrictor, is plugged.

I still wonder about the fuel level too. I know you did the clear tube test, but if the pilot circuit is working then the issue would be that the fuel level is too low in the bowl and so fuel isn't able to be pulled into the carb.

flybox1 · « **Reply #16 on:** December 05, 2018, 10:59:41 am »

Quote from: Jnel on December 05, 2018, 09:57:05 am

Good afternoon gentlemen.

I remove the idle jets from all 4 carburetors they're in good shape andI replaced them turning each one out 1 and a 1/2 turns.
These are not jets, they are mixture screws, or (IMS) idle mixture screws.

I adjusted the floats in all 4 carburetors. I use the clear to method and they're all reasonably good.
Reasonably, or correct? fix them if they are not

When I put them back together the number for carburetor did not overflow. So this was a good sign.

With regards to the choke situation, it is fully closed when I apply the choke. Have a good strong battery and it turns over really well.

I forgot who it was who said this... but somebody said if I give the throttle a couple of quick snaps that I should see fuel coming out of the accelerator pump nozzle. This is not happening. I engage the starter and gave the throttle a few more pumps and still nothing out of the accelerator pump nozzle. These carburetors are bone dry during the starting process, So I think I have a Fuel issue. I can't even smell fuel.

Starting fluid does make it fire but and only runs for just a few seconds. After the starting fluid Burns off ... Nothing!

There is definitely Fuel in the bowls, But it's not making it's way up to the upper part of the carburetor. Frustrating!

Thanks for all the comments. Its helping.

Regards,
Jnel

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you need to TAKE OUT your jets. Main jet and emulsion tube turns out with a flathead screwdriver. separate them, clean all their holes.
PULL out the pilot jets. clean and clear all the holes. replace them the same way they went in.

Take off the accel pump bowl(3 screws) on the bottom of carb bowl #2
Remove the spring, and accel pump diaphragm. verify they mickey mouse ear holes on the diaphragm are clear. ensure teh diaphragm itself is not damaged or ripped.
on the accel pump bowl-spray carb cleaner thru the side holes to clear them. one of the holes will allow cleaner to spray thru the check valve in the middle bottom of this bowl. if it doesnt...ultrasonic cleaner/simple green will clear it.

On the bottom of the#2 carb bowl, where the accel pump bowl attaches, you will see a hole where fuel travels up to another check valve on the mating edge of the bowl...(supposed to be a small oring here)..spray carb cleaner up the side hole to clear out the check valve. if it doesnt...ultrasonic cleaner/simple green will clear it.

between the carbs on the rack, are fuel delivery tubes. the three upper ones are for filling the carb bowls. the other 3 smaller ones are for circulating fuel in teh accel pump circuit. remove these 3 black tubes and clips (small brass tubes inside each of these....dont lose or crush them when taking them off)
youwill have brass hose barbs exposed....you need to spray carb cleaner into these (plug the opposing side) to ensure the accel pump squirters (in the carb throat) are not clogged...
Put everything back on the way you took it off.

Go here for pictures and more information...feel free to PM me if needed...

http://forums.sohc4.net/index.php?topic=48858.0

flybox1 · « **Reply #17 on:** December 05, 2018, 11:01:32 am »

here is another good one...
Read it thru before you start your work

http://forums.sohc4.net/index.php?topic=146893.0

Jnel · « **Reply #18 on:** December 05, 2018, 01:02:39 pm »

I want to thank everyone that has replied to this post. FLybox1, Bankerdanny, TwoTired, bryanj, and DonR... Thank you all for the help and advise.

In a PM to flybox1 I was mentioning that I was frustrated with this carb BS. As I was telling him, I put a lot of time and effort into this project over a long period of time. I was hoping for a little noise out of this thing so I could be motivated to move on, spend some more money and be happy. But that just ain't gonna happen this time home.

My work schedule is 2 months at work and one month home so you can see how these projects take a long time to complete. So if this sounds like I'm giving up... Not a chance... not even close.

But I do have to rethink my situation. My thoughts are that I will send these carbs to a professional who can do this job much better than me. In two months I get get home and put them back on. Then maybe I will hear the noise that I've been waiting for for almost two years.

Anyone got any ideas on what sucker, I mean professional, would be a good choice for this project?

I just want them right. No vapor blasting, painting or powder coating. I just want it to run.

Your thoughts will be greatly appreciated.

Best Regards and thank you all once again.

John Nelson

flybox1 · « **Reply #19 on:** December 06, 2018, 07:34:44 am »

No matter who works on them, you would still need to make final, small adjustments for them to operate with YOUR bike (IMS adjustment, vacuum sync, etc), so, keep at it. I think sending them off wouldnt gain you much.....i bet you are really close!!!

I understand your frustration, but there are many here who are happy to help.
So, since we cant be there seeing it, be as detailed as you can in your posts so we don't have to go searching above for info, include all setting changes before and after, and any results from those changes. If you weren't on the other side of the US, im sure it'd take us just a few hours

Jnel · « **Reply #20 on:** October 19, 2019, 07:29:21 pm »

Its been a long time since i posted. I thought I would let you all k ow i rode the bike yesterday. It hasn't run under its own power for 19 years. What a feeling. Just shy of 3 years since I started working on it. I had a stupid grin on my face all day. Thank you all for the support in the last years. I know now that it was all worth.

Regards,

Jnel

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Scott S · « **Reply #21 on:** October 20, 2019, 05:47:35 am »

Very nice! Congrats!

Don R · « **Reply #22 on:** October 20, 2019, 06:57:20 pm »

I know that feeling when you get that ride you've been waiting so long for. It's good to see it go.

BenelliSEI · « **Reply #23 on:** October 21, 2019, 08:40:24 am »

Well done, everyone on here get’s it! Nothing better.......

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Author Topic: 1978 F 750 Starts with help Can't keep it running (Read 2400 times)