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Help! Nighthawk won't run after carb rebuild.

Old 08-16-2015, 12:20 PM
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Help! Nighthawk won't run after carb rebuild.

Hey I know this is a superhawk forum, and I am inquiring about help on a nighthawk, but you guys were excellent help with me when I used to own a superhawk so I thought maybe you guys could help me again...


Let me explain this situation...

A few weeks ago I was riding my nighthawk and I pulled over to get gas, filled up, and took off from the gas station. Moments after pulling out of the station my bike would not run right at all. It refused to rev past 4K rpm's and if I tried to give it a spurt of gas it would prefer to just cut off. I had to feather the gas and the clutch 3 blocks down from the gas station to get to my house and it cut off on me 7 times.




So I dumped the gas out, put fresh gas in, and it made no difference. So then I took the carbs off and cleaned them up, they weren't terrible but I assume some thing got clogged in there. I also replaced the spark plugs with NGK Iridium. This is where it all went wrong... On spark plug #2 (From left to right) The new plug didn't screw in properly, it created its own threads. I didn't even notice this until I compared the alignment with spark plug #3 and they were definitely different. So after about an hour of trying to get this spark plug on its own threads, I screwed it in and noticed it was nearly identical except it was still off alignment by maybe 1/6 of an inch. (Leaning to the left) I tried starting the bike but doesn't wanna run at all. It will kind of sputter and run while I hold the starter motor, and I heard it backfire twice (Made a weird wurble noise at the end, lmao)




Any way, I am now screwed. I assume my bike isn't firing because spark plug #2 is not threaded correctly. How do I fix this? And is this even my problem?
Thanks!!!!!!!!!! any help would be appreciated, I need to fix this asap as I use it to get to work and back.
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Old 08-16-2015, 01:02 PM
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Mmm... Thats not cool.

Multiple things worry me. One is that all the spark plug fiddling and creating new threads could potentially be sending strings of aluminum down into the cylinder. You may considering vacuuming it out (tape a piece of rubber hose to a wetvac and stick the hose down in the spark plug hole). May be overkill but i'm a little cautious about engine internals.

If you really want to permafix the spark plug hole then you need to pull the head and have it helicoiled or keenserted (preferred).

Hopefully you can get the plug to thread in properly by going real slow, work it in a turn, then out a turn, and recut the threads. Remember that new plugs have a crush washer on them. The plugs need to be torqued down (tightened real snug) so the washer crushes and you achieve proper compression in the cylinders.

Sometimes people stop tightened the new plug when they first feel a bit of resistance, but this is the point when the crush washer makes contact with the head. Thr washer still needs to be crushed.

Do you have access to a compression tester? If not, can you find out if auto zone will rent one to you? (Hopefully one with multiple threaded adapters so you can find the threads that match your spark plug).

James
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Old 08-16-2015, 02:08 PM
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Originally Posted by thedeatons View Post
Mmm... Thats not cool.

Multiple things worry me. One is that all the spark plug fiddling and creating new threads could potentially be sending strings of aluminum down into the cylinder. You may considering vacuuming it out (tape a piece of rubber hose to a wetvac and stick the hose down in the spark plug hole). May be overkill but i'm a little cautious about engine internals.

If you really want to permafix the spark plug hole then you need to pull the head and have it helicoiled or keenserted (preferred).

Hopefully you can get the plug to thread in properly by going real slow, work it in a turn, then out a turn, and recut the threads. Remember that new plugs have a crush washer on them. The plugs need to be torqued down (tightened real snug) so the washer crushes and you achieve proper compression in the cylinders.

Sometimes people stop tightened the new plug when they first feel a bit of resistance, but this is the point when the crush washer makes contact with the head. Thr washer still needs to be crushed.

Do you have access to a compression tester? If not, can you find out if auto zone will rent one to you? (Hopefully one with multiple threaded adapters so you can find the threads that match your spark plug).

James


No compression tester. Off to auto-zone when I get some time off at work. I was told by a few people that even if cylinder #2 is not firing cause of the threads, that the bike should still run, just not well. If it should still run, I have another issue on my hands. To add to that, the motor is spinning way faster then I remember it used to. I assume due to low compression?
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Old 08-16-2015, 02:24 PM
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If the plugs aren't seated, then yes, low compression.

James
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Old 08-16-2015, 02:37 PM
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Originally Posted by thedeatons View Post
If the plugs aren't seated, then yes, low compression.

James


Will the bike run at all if all the cylinders have good compression except for cylinder #2 with the bad threaded plug? And to add to the vacuum thing. I did vacuum the cylinders out a little bit. If I could get a smaller hose I will stick it down there as well.


*EDIT* And I just had a thought about what you said about the spark plug washer. How tight should I turn the spark plug? I just tightened the new plugs until I felt resistance and then did like one extra turn. By the way, spark plug #3 and #4 I can still see spark plug threads. On #1 and #4 no threads can be seen. But #3 and #4 are pretty tight.

Last edited by Chrisguilday; 08-16-2015 at 02:57 PM.
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Old 08-16-2015, 04:51 PM
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I tighten my plugs with a 3/8" ratchet until they stop. Try putting an old plug back in and turn it until it stops. That will give you a good idea of what it feels like because that washer is already crushed. Make sense?

The bike should run on 3 cylinders, but who knows

James
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Old 08-16-2015, 05:08 PM
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Originally Posted by thedeatons View Post
I tighten my plugs with a 3/8" ratchet until they stop. Try putting an old plug back in and turn it until it stops. That will give you a good idea of what it feels like because that washer is already crushed. Make sense?

The bike should run on 3 cylinders, but who knows

James


Old plugs are long gone... They weren't NGK iridium's though. Maybe I just need to go to the shop and by 4 $3 NGK plugs. I think they were the cheap NGK ones any way.
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Old 08-21-2015, 06:24 PM
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So a quick update... I had a certified mechanic come check out my bike.


Main reason the bike wouldn't start was because the spark plugs were not torqued enough causing low compression.


Second of all spark plug hole #2 and #3 were both partially stripped. Mechanic said there are enough threads where can he tap it for me without helicoil or timesert.


He is picking it up tomorrow and bringing it to his shop, he is going to charge me $100 to tap the plug holes. Seems like a very fair deal so I'm going with it. Hope he doesn't steal the bike, if he does... I know where he works. Lol
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Old 08-21-2015, 06:42 PM
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In the future when this happens, assume watery gas.

Drain the tank asap, then drain the float bowls of the carbs. Water is still heavier than gas and sinks right down there.

Take off the tank and shake it upside down to get it dry. Then start with fresh gas from a DIFFERENT station.

If you are not running a fuel filter now is the time to save yourself heartache and install one. (or several but one off the petcock should work.)

Spark plugs can be a pain. Better to be careful and take a long time than this result but of course you know that already. Probably everyone has done that at least once.
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Old 08-21-2015, 07:50 PM
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Originally Posted by smokinjoe73 View Post
In the future when this happens, assume watery gas.

Drain the tank asap, then drain the float bowls of the carbs. Water is still heavier than gas and sinks right down there.

Take off the tank and shake it upside down to get it dry. Then start with fresh gas from a DIFFERENT station.

If you are not running a fuel filter now is the time to save yourself heartache and install one. (or several but one off the petcock should work.)

Spark plugs can be a pain. Better to be careful and take a long time than this result but of course you know that already. Probably everyone has done that at least once.


It was probably water in the gas the whole time. I am here in Tampa Florida. We had really bad rain for 2 weeks and it flooded most of Tampa. The streets looked like oceans.


I assume some water managed to get into one of the gas tanks at the gas pump. Although the gas looked blue-ish like diesel fuel when I emptied it. Still doesn't explain why it wouldn't run right after I emptied the tank. I ran the motorcycle out of gas to empty the carbs. Probably not the smartest thing to do.


We will see what happens when I put the plugs back in correctly on Sunday.
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Old 08-26-2015, 05:17 PM
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So here's an update...


Apparently there was still gas in the tank from the first time I emptied it. Which seems almost impossible but maybe there was gas in the reserve. This gas definitely had water in it and I wasn't aware as I thought I emptied it.


After cleaning the carbs initially I put every thing back on. Found out about the bad plug holes. I had those fixed a few days ago. And I decided to take the carbs off again because the guy that fixed my plug holes said he saw water in my tank still.


Sure enough the carbs were gummed up with watery gas. Cleaned them out, put every thing back on. Spark plugs were seated correctly. Petcock was flowing correctly. I have spark as well...


And the bike still won't start??? I did a compression test and it's indicating 30 psi on cyl #1 and 100 psi on cyl #4?? How did I lose complete compression in 2 weeks of not even riding it? This bike would scream to 140 mph no problem before. I just can't see it losing compression for no reason.


To add to this... I purchased another 83 nighthawk recently. Did the same tune up on that one as I did with my 86 that's having issues. Both bikes had a hard time getting fuel to carb #3 and #4, the bike leans to the left away from those carbs so I don't know if that effects it. Both bikes refused to start with or without starter fluid no matter what I did. However, I did attempt push starting the newly purchased bike and it fired instantly and ran perfect. The original bike I have not yet tried to push start... I wonder if that will fix it lmao.


Does that make any sense?

Last edited by Chrisguilday; 08-26-2015 at 05:32 PM.
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Old 08-26-2015, 06:06 PM
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And yes batteries were charged fully and checked for issues on both bikes.
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Old 08-26-2015, 08:57 PM
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Well, firstly, did you shake the tank upside down or just do the hope for the best syphon thing. Water is heavier than gas and every drop at the bottom will be water and crud (as you are learning).

When you start the bike, skip down to your local auto store and invest in a couple cans of starting fluid.

Almost every motor I have rescued from drowning needed it. If that doesn't work (it will) you gotta chase spark.

But for now just spray it into the airbox or intake AS YOU TURN IT OVER.

Case solved.
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Old 08-27-2015, 11:19 AM
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Originally Posted by smokinjoe73 View Post
Well, firstly, did you shake the tank upside down or just do the hope for the best syphon thing. Water is heavier than gas and every drop at the bottom will be water and crud (as you are learning).

When you start the bike, skip down to your local auto store and invest in a couple cans of starting fluid.

Almost every motor I have rescued from drowning needed it. If that doesn't work (it will) you gotta chase spark.

But for now just spray it into the airbox or intake AS YOU TURN IT OVER.

Case solved.

Yes I did shake the tank upside down for like 5 minutes trying to get every last drop out.


I've already tried that. Both bikes refused to start with starter fluid and both bikes have spark. Both bikes batteries are dead now due to me trying to start them for so long. In desperation I thought hell with it, I'll try one last thing and jump start the newly acquired bike and it jump started instantly. I haven't had the chance to try and jump start the bike that this thread was originally for.


Both bikes went through identical process to get them running.


I'm just wondering if maybe I'm doing some thing wrong to not allow either bike to start with the starter motor. I will try to bump start the 1986 nighthawk and see if that works when I get a chance.

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Old 08-27-2015, 11:42 AM
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Also any reason why both of the nighthawks have a problem getting gas to carb 3 and 4? When I drain #1 and #2 a good flow of gas comes out. With #3 and #4 hardly any gas comes out.


The newly acquired bike obviously doesn't have this issue any more as the carbs properly filled with gas when I bump started it, so now it starts with the starter motor fine and is running perfect. The most obvious fix for an issue like this is a bad battery. But both batteries were tested and were 100% charged.
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Old 09-05-2015, 05:41 PM
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So they start with jumper cables, but not with the bike's own battery?

If that is the case i would try a new battery (no matter what the charger says).

If they bump start but don't start with a good battery then you may have a weak starter.

James
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Old 09-08-2015, 05:20 PM
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Originally Posted by thedeatons View Post
So they start with jumper cables, but not with the bike's own battery?

If that is the case i would try a new battery (no matter what the charger says).

If they bump start but don't start with a good battery then you may have a weak starter.

James


Not quite. After tinkering with both for a while now... The 1986 nighthawk that I was having issues with originally won't start at all period. The 1983 nighthawk will bump start every time instantly, but will only some times start with the starter, and only if its warm. I don't know why, maybe the A/F is messed up or some thing.


Just recently tried bump starting the original 1986 one and it won't bump start, so I have no clue what's wrong with it. Tried every thing in the book so far. I have pretty much given up at this point as I think the next step would be to bring it to a dealer, which isn't even an option as the bike isn't quite worth the dealers fees.
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Old 09-08-2015, 05:28 PM
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So you still haven't done a compression test on each cylinder? This is one of the first things i would check on an old bike that has trouble starting.

James
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