Question about Honda CB 750 Nighthawk Motorcycles

2 Answers

Carburetor problem or ? 1975 Honda CB750K, #4 Cylinder about 160 degrees F cooler than other cylinders. Compression all about 135 psig, overhauled the carbs fuel in bowl is clear and levels are #1 & #3 is 45ml (1.5 oz), #2& 4 is 40 ml (1.4 oz) Used a Fluke non contact thermometer and got the following temperature on fin at 12:00 position above exhaust pipe, outside temperature was 25 degrees C ( 77 degrees F), bike brought up to temperature and at idle not moving #1& 2 read 134 degrees C (273 degrees F) #3 read 132 degrees C (270 degrees F) #4 read 44 degrees C (111 degrees F) Checked spark and was strong, has an electronic ignition system HELP very little hair left?

Posted by on

2 Answers

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Master
  • 3,567 Answers

Be certain that fuel is getting into the float bowl on the bad carb. If so, and the fuel level is at the correct height, the problem would be either the slide is not raising as it should, the main jet is plugged up or there is a blockage in the air clearer/manifold.
The compression is good so a valve can't be stuck. You said you have spark. The only thing left is a fuel problem or air problem. Please rate my answer. Thanks.

Posted on Aug 19, 2010

Testimonial: "Thanks I will check the slide and air manifold"

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 5 achievements.


    An expert whose answer got voted for 20 times.


    An expert who has written 20 answers of more than 400 characters.

  • Expert
  • 79 Answers

Just fixed a similar problem on my '77 GS750. No temp gauge, but one cylinder was cooler than the rest (spit test!). Turned out to be simply a duff HT Cap. I had also checked the spark, but it looked as 'blue' as the others.
I would also check the temp on the downpipe for each cylinder as this would eliminate any issues with the thickness of the fins/heat path etc.
Does the bike run well?
Hope yours is as easy to fix as mine!

Posted on Aug 19, 2010

Testimonial: "I will check high tension leads, bike does run fine"

1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Stop oil from getting into carburetor and cylinder

It will be very helpful if you post the type of car you are having problems with so we can try to help. But rule of thumb is that if you are getting oil into cylinders, your piston ring or rings are failing... Depending on the mileage of your car that means that the engine needs an overhaul. A good mechanic can do a compression test on your engine for a very reasonable price so you can get an estimate of the parts and labor needed. Good luck!

Nov 02, 2015 | Cars & Trucks

2 Answers

96 Honda Civic making a popping noise when I release the clutch and third gear

Reasons for popping noise:
Popping noise could occur due to the malfunction in the ignition system, leaky valves, weak cylinder compression, carbon accumulation in the combustion chamber or lean fuel.
1. Ignition system malfunction (Misfire).
- The ignition timing.
- Spark plug gaps.
- Use colder type spark plugs.
- Ignition module and ignition coil.
- Distributor cap and rotor.
- Spark plug high tension cords.
2. Cylinder compression:
- Check valves clearance.
- Perform cylinder compression test.
3. Fuel system (For lean state).
- Check fuel filter for clogged.
- Check fuel injectors.
- Check fuel pump pressure.
- Check fuel regulator.

May 04, 2015 | 1996 Honda Civic

1 Answer

My boat motor has low compression @ number 1 cylinder how can I fix it

2 possibilities:
-1 Your head gasket is burned. Caution, some Mercury engines have no head gaskets. I could tell if I had your serial number.
-2 Your cylinder has seized. If it's the upper cylinder, you'll have also to check your cooling system! Look at your spark plug if you can't see some 'aluminum' deposit on it. Or, inspect the inside of that cylinder with an endoscope.
Such an old engine is mostly not worth a complete overhaul. So, in case of seizing, just hone that 1 cylinder and use a new piston with rings.

It's in any case better not to use that engine in this state.

Mar 06, 2015 | Seloc Mercury Outboard Repair Manual, 1965...

1 Answer

Low overall compression in 1996 honda accord 4cyl 129.75 psi avg.

the compression pressures are on the low side. The indications are worn rings as the pressure readings come up when the ring seal is improved with the addition of oil. The bores will be worn in a taper and if the head was to come of there would be a noticeable lip where the top ring stops in the cylinder
rings and cylinders wear equally but rings suffer from a loss of tension, and an increased ring gap that allows more compression to escape to the sump
Do you need to do something about it--
if there is an oil consumption problem( smokey) then yes
If the economy is acceptable to you then --no --not immediately
What should you consider in making a decision----
1. good engines are available from japanese spares ( imported engines with less than 30.000klms on the engine for a fair price
2. consider what is termed a "short motor" which is the block,crank, pistons ,rings,oil pump and sump all new
What you should not consider is a quickie fix--set of rings and nothing else as this will cost you more in the long run.

Feb 20, 2015 | 1996 Honda Accord

1 Answer

What is the Compression supposed to be for a 1987 Toyota Pick up 22R with carb, 4 cyl.???

A new engine would be about 180 psi for each cylinder. As the miles add up and wear occurs, compression will get lower. The important thing is that compression is even and balanced-lowest compression reading should be within 75% of the highest cylinder's compression. Some Toyota engines had a minimum allowable compression of about 135 psi, but if compression is balanced, you could have average compression as low as 125 psi and engine would still run good, some loss of power but still acceptable, and oil consumption would not be that bad.
If cylinder compression is below 120 psi as an average, you should be looking into a rebuild event-rings and valves need attention. If any cylinder is below 100 psi, it may not even fire, certainly will produce no power, and could be a head gasket failure, very worn rings, or valve problems.
Remember the important thing is to find compression readings that are very close to each other. I have an '87 Sentra with 75,000 miles(true!)-lowest comp. is 160, highest is 165 psi-runs great, good power. Also a '79 Datsun pickup (with god only knows how many miles-about 200,000 maybe). Compression is about 125-135 psi, fairly well balanced-noticeable loss of power, very little oil burning, still runs fair to good-dependable, at least.
That should give you an idea of what to look for. Good luck.

Aug 29, 2013 | 1987 Toyota Pickup

2 Answers

My chainsaw starts and idols ok ,when I try to cut a log it bogs down and stalls off

Sounds like a carb problem. My 310 stihl did the same thing. Rebuilt the carb and now it will cut the gates of the hinges off of H**L

Sep 22, 2011 | Husqvarna "Chain Saw - 16" Bar, 3 Hp

1 Answer

Computer diagnosed o2 sensor, but problem is worse since changing, engine reves for about 1/4 mile before shifting

Check the transmission. The O2 was a problem but wasn't the root cause of teh problem. Also check the compression on all cylinders to make sure it is within 10 to 15 lbs of compression on each cylinder. ie If you have 135 psi on cylinder 1 all the cylinders should be between 125 and 150 psi. Extremely high or low psi on anyone cylinder when compared to the rest will cause this problem. You have described a situation where the motor is only running on 3 cylinders in a 4 cylinder motor or 4 to 5 cylinders in a 6 cylinder motor. The higher RPM is needed to get the same speed and result as a lower rpm in a motor using all cylinders on the motor.

Feb 05, 2011 | 1996 Chevrolet K1500

1 Answer

1997 honda accord vtek 2,2 I have engine compression in one of 125 and nothing in the other 3 any suggestion

Did the timing belt break? Or did it over heat? ethere way you will need to do a valve job on the cylinder head, but before you do that, do a wet cylinder compression test, shoot some oil in the cylinder's then do a compression test, if compression goes way up, then you have bad piston rings and the engine will have to be overhaul or replace.

Jul 05, 2010 | 1997 Honda Accord

1 Answer

I have a 1975 dodge d100 and and the carb shoots at me

You may have a bad intake valve. To find out you need to do a compression test on the engine. If the compression of the cylinders are more than 10% of the difference in all cylinders it will need to be overhauled. If you have a compression gage try that first, you can pull the plugs and see what plug are wet and that will tell you which cylinder is leaking gas.

Jun 01, 2010 | 1984 Dodge D150

2 Answers

Ignition problem with CB750K Honda

Please check carbs again. Gunk sometimes hids. Clean out orifice's
(vacuum inlets) real good, then spray with air hose. It takes time to get a bike ruuning good after setting over 6 months.

Oct 15, 2009 | Honda CB 750 Nighthawk Motorcycles

Not finding what you are looking for?
Motorcycles Logo

Related Topics:

224 people viewed this question

Ask a Question

Usually answered in minutes!

Top Honda Experts

Arnie Burke
Arnie Burke

Level 3 Expert

4514 Answers


Level 3 Expert

75077 Answers

Gino Cussen
Gino Cussen

Level 2 Expert

216 Answers

Are you a Honda Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides