Help 20 year old Nighthawk S

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carydf
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Help 20 year old Nighthawk S

#1 Unread post by carydf » Sun Feb 24, 2008 6:16 pm

I have a 20 year old Honda Nighthawk "S" with very few miles on it that I am trying to get running again. Its been idle for a while (years). I'm sure I'll have more than one question.

The pistons are moving, the oil, filter, air filter, and spark plugs have been changed, the carb has been cleaned and a couple of carb parts have been replaced. I have a charged battery. Cleaned the tank and petcock.

All systems look good. It turns over and with starting fluid it "almost" catches. Note: There was a dead spot when I started turning it over and when it stopped on that spot I had to move the pistons to get it to turn over again. Does not do this anymore but it might be a clue. I checked and at this point there was gas in the carb bowls. Frustrated I went back to square one.

I put a clear tube with inline filter in the gas line. I drained the carb bowls of gas and checked there was a spark. Vague smell of gas on the plugs but not much of a smell. I'm also I'm not sure how much of a spark there is supposed to be. I assume its a good spark.

I tested the petcock and it works when disconnected from the carb. BUT when its hooked up to the carb it does not work the air out of the fuel line (not enough suction?).

Suggestions on where to go next?

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#2 Unread post by Wrider » Sun Feb 24, 2008 6:54 pm

The suction thing sounds about right... Like there's not enough. It might be the piston rings. If it's been sitting for so long the piston rings might not be sealing well against the cylinder walls anymore, so you might be looking at a top end rebuild too...
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#3 Unread post by Johnj » Sun Feb 24, 2008 9:00 pm

Do you know how to do a compression test?
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#4 Unread post by MrShake » Mon Feb 25, 2008 10:03 am

+1 on compression...

If you have spark, and you have fuel, and you have compression, you SHOULD have GO
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#5 Unread post by Gnarlyroad » Mon Feb 25, 2008 11:32 am

When starting my nighthawk after its been sitting for a while I know that it does not like any throttle applied at all. Choke it and turn it over till it starts. Don't give it any throttle tilll its warmed up a bit. If you throttle it and it dies. Start it up again without any throttle leaving the choke on. Hope this helps!

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#6 Unread post by safety-boy » Mon Feb 25, 2008 12:54 pm

+2 on compression.

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What I found out so far

#7 Unread post by carydf » Mon Feb 25, 2008 2:28 pm

Thanks for the replies. Very grateful for your help and advice.

I played with the gas line and I have fuel in the carb bowl now. I do not have anything on hand to test compression. I will find borrow one as soon as I can. I pulled the two left hand side spark plugs and there is compression. How much? I do not know. Too much for me to keep my finger over the plug hole, not enough for it to suck my whole finger in. Didn't want to get my finger sucked in either

I read somewhere that you can put carb cleaner in the cylinder to clean out the gunk. Is that true?

Next clue (while I search for a friend who has compression tester). With gas tank disconnected and the plugs reinstalled I hit the starter (choke off) and it fired for a second or so. There does not seem to be any real gas getting to the plugs. The smell is the lub I've been feeding it to keep the cylinders from locking up.

After writing this reply I went outside and tried to start the bike again. With choke on and fuel on, there was a hint of firing. I let the bike sit for another ten minutes and again the same thing. Just a hint of firing, and then back to just the noise of the starter motor.

Thanks again.

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#8 Unread post by MrShake » Mon Feb 25, 2008 3:39 pm

I would check all your cylinders with your finger for compression. Its not the best of options, but you will be able to tell if there is a suck valve causeing a complete loss of compression.

I think you said you checked for spark... did you check all plugs? How did you test for spark?
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#9 Unread post by carydf » Mon Feb 25, 2008 4:09 pm

I'll check again to see if there is spark on all four as well as a finger compression test on the other two.

I was just out for an hour and when I got back I tried again to start it again. Choke on, gas on. When I hit start it caught for a tiny bit and then died.

I'll wait an hour and try with choke off.

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New information (no gas in carbs)

#10 Unread post by carydf » Tue Feb 26, 2008 12:21 pm

I checked and there is spark/compression on all four cylinders. I can not hold my finger over the plug hole. The outgoing pressure is too much. I guess this means there is a fair amount of compression.

I took each spark plug out one at a time, connected it to the plug wire, and clamped it to a good ground on the bike. There was spark on each plug.

I have not found a real compression checker yet. I did make sure to check each spark plug to see if it smelled like gas and none of them really smelled like fresh gas. (I had the clean up the work area to get all the spilled gas/chemical fumes out.) Each plug smelled more like the fluids that have been used to keep the pistons free than gas.

Any suggestions on how to check the carb? There is gas in the bowls. I can easily reach the drain. How high should each carb bowl be filled? I can check using a long clear tube and see how much each bowl is filled. At the moment it not filled very much. Only about 1/4" of fuel in the bowl. Should it be filled?

I pulled the cover off the top of the carb and checked the throttle valve. Should it smell like gas? I assume it should. If it does not smell like gas, where/what to check next?

Again if I let it sit for a while and then try to start it catches for a few cycles and then dies.

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#11 Unread post by coffee_brake » Thu Feb 28, 2008 12:50 pm

In case you haven't already....

Simple check: the big idle adjuster screw....wherever it's set, have you turned it a few times either way from there and tried to start it? When I went through the carbs on my '92 NH the first time, I thought everything in the world was wrong with the bike after it wouldn't start...but it was that big idle screw that had gotten way out of adjustment.

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#12 Unread post by XJRJohn » Fri Feb 29, 2008 2:59 pm

A trick we use to get superdreams to fire.....Use a hypodermic syringe to inject a drop of fuel into two cylinders ,replace plugs and give it a go.Superdreams were terrible for not sucking fuel through,but after we put a drop of fuel in they started easy.xjrjohn
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#13 Unread post by carydf » Sun May 04, 2008 2:41 pm

I ended up buying new carbs on Ebay. After much effort found the carbs had some clogged inner parts (channels) that would not clear. Don't have the expertise to drill them out nor did I want to pay local shop $250 to do it.

Needed a few parts for the Ebay carbs. The choke needed some parts swapped out from original carbs but nothing serious. Total investment in new carbs was $25. Vents all looked clear, needles,jets, and bowls looked clean.

Bike now starts but will die if I either shut off the choke and/or let it idle below 2k (with choke on). Gas is dripping into the air fliter box. I assume because the choke is on full.

Smoke coming from the tail pipe smells like water vapor instead of exhust. Not sure if something else is wrong. Could water be in the bike from sitting for 20 years? Could be water in the fuel? Suggestions welcome.

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#14 Unread post by BuzZz » Sun May 04, 2008 3:50 pm

Turn the fuel petcock to reserve, that should bypass any leaky diaphram issues and supply fuel to the carbs. Air bubbles in the fuel line don't mean much in relation to 'suction' from the carbs, the floatbowls are fed by gravity, turning the petcock to prime should solve any delivery problems to the carb for now. Manifold vacuum opening the petcock can be addressed later if it is a problem.

If it 'almost catches', it is firing, I assume. So you have spark and compression happening at approximately the correct time... that leaves fuel. It really sounds like your carbs are varnished up, your floatbowls aren't filling enough or some other carb problem. Looking at the guts of a carb won't really tell you if it is 'dirty'... it's not dirt your looking for, it is a clear coating of varnish reducing the diameter of the jet openings. A few thou of buildup inside an orifice of several thou will drastically affect fuel delivery. Compressed air won't remove it, neither will most carb cleaners the public can buy. You have to physically get inside the jets and clean it out, without scraping or scratching the jet orifice. Use a material that is softer thatn the brass that the jets are made of. Or find a shop with an ultrasonic cleaner and get the entire bank of carbs cleaned. Or replace the jets with new ones.

A compression test on an engine that hasn't run, especially in years, is useless IMHO, the more P.C. would say 'unreliable'. After you get it to run and put some heat into it, slosh some oil around the internals and loosen up the rings and slap the valves against the seats a bit, then a compression test can tell you something.

I would say you still have carb issues. Give them a proper cleaning and Goodluck, eh.
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#15 Unread post by carydf » Sun May 04, 2008 5:45 pm

I'm a little confused about the last post from BuZzz. I am past the "almost catches" and onto getting to run without the choke. Was the post in reference to the original post or the update from today?

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#16 Unread post by BuzZz » Mon May 05, 2008 12:58 am

Sorry Man, I sorta zoned off on the first post and skimmed the update, so my bad. But I still think you have fuel delivery problems. The low speed or idle circuit is not giving up enough fuel to keep it running with the choke off. Maybe the floats are set too low and there is not enough fuel in the float bowls. Maybe the passages in the carb bodies are blocked, or the jets are wrong or something like that. I don't know what carbs your bike has (and I'm too lazy to look it up :mrgreen: ) but they may have idle air screws you can adjust externally.
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