Honda Cafe-Hints, Tricks and Info

[Home]-[Honda 750]-[Twin Carb Systems]-[Honda Cafe]-[Harley]-[British]-[High Performance Ignitions]-[Pawn Shop]-[New Products/Coming Soon] 

  Click to go Back to Honda Cafe Index 

________________________________________________________________________________________________________________________________________________________              

 

test bike 1111.JPG (325280 bytes)      test bike.JPG (332350 bytes)Rat bike   ( test bike )


We have several bikes for testing purposes. This is one beat up nasty Honda cb750 ( stock motor ).
This bike has 34,000 miles and has led a hard life ( especially around our shop )
This bike has always been able to fight off the most determined challengers. 

So, why does this bike run so good ?

Motor is bone stock with 34,000 miles
Tri - Y  4-2-1 exhaust ( open )
Modified spark plugs
Carb's are stock ( 1974 )
Jetting :
Stock pilots
.007 removed from the underside of the slides
Needles 1 click from full rich
140 mains
Open velocity stacks

 Cycle X power arc ignition with aggressive advance curve.
The addition of our ignition was the final step needed to turn this bike into a real sleeper.
This thing hauls ass.

 

 

Before a person can begin to fine-tune the internal combustion engine, many people have issues with their 30 plus year old project bikes. We can talk about a lot of fun topics like exhaust systems, carburetion, ignition systems, etc…. but troubleshooting is sometimes annoying without a systematic approach. We at Cycle X have a system we follow every time an ill running bike is in our shop.


THE POWER TRIANGLE:
 The power triangle is nothing new but needs to be remembered when the going gets tough diagnosing poor running bikes.
Motor must be in good, sound condition. (Duh.)
Ignition must be in good, sound condition. (Duh.)
Carburetion must be in good, sound condition. (Duh.)

 

MOTOR:
 Valve adjustment should be checked or adjusted. Reminds me of a story. We had a drag bike with big, overlapped cams and it had 16-to1 compression. Because of the cam profile we had a little over 120lb’s compression. But the compression increased with the RPM of the motor. (It’s a cam thing.) We could alter the compression readings by setting the valves looser. (Cutting back on duration.) The looser we set the valves, the faster the bike went. And the compression changed also. So, if you want an accurate compression reading. Make sure to set your valves.

 

CHECKING COMPRESSION:
 Open up throttle. Turn motor over 4 times and record readings. Do not be concerned with the readings being high or low. Be concerned that the readings are within plus or minus 5 percent of the average. Remember the cam profile story. NOTE: Over-head cammed motors compression readings can be affected by cam chain stretch also. NOTE: An abundance of oil in a cylinder will raise compression. (If you’re motor was upside down or on its side.)

 

IGNITION SYSTEM:

We like modern high-powered ignition systems for obvious reasons but if you have points and stock coils here are some tidbits of info. Stock coils produce approx. 10,000 volts. Internal combustion engines need 14,000 to 18,000 volts to complete the burn properly. Points start to go out of adjustment after about 200 miles. Points have also been the primary cause of detonation in higher performance motors which connecting rod breakage has been seen.

 

DO’S AND DON’TS:
 Solder all connections. 1/10 of a volt can be lost with each connection without soldering.

Check spark plug caps. 5K ohms is good.
Clean and set points to .015-point gap.
Lube advance unit cam lobe. If you don’t, your ignition timing will retard.
Check charging system. Low battery = Low spark.
Use a timing light. We time to the full advance marks. Timing lights can be used to detect misfires in your ignition system. If you suspect a problem… Hook up a timing light to your bike. Start the bike and flash the timing light on your leg or arm. You will see and here the misfire.
Never splice spark plug wires to get more length.
Modern ignition systems have big spark, consistent timing and zero maintenance.

Now that you have addressed your motor and ignition system the carburetion system will hopefully be a breeze.


CARBURETION:
 Check needle/seat and float adjustment. The amount of fuel in the float bowl will have an affect diagnosing rich or lean conditions.
Check for intake manifold leaks. Spray carb cleaner around the intake rubbers to detect fluctuations in the motors RPMs. (We see this problem a lot.)
When jetting carburetors start from the bottom (Idle.) and work your way up.(Main jet.) Check your jetting at ¼, ½, ¾ and full throttle. This jetting thing is part common sense and experience. Mikuni has a very detailed book on jetting carburetors if you run into trouble.

 

 

Gasket Installation:

Here is what we notice...

When we are reconditioning Honda motors we notice very few cylinders, heads, covers, etc... are true or flat. Actually, The top side of the head ( cam side) is more inconsistent than the bottom. Valve covers can be inconsistent also. Chroming the valve cover can leave a untrue surface, because the chroming process can at times, leave a dripping texture on the gasket surface.

Previous gasket replacements can and have left scraping marks, which can cause problems. We are also not fond of the factory cylinder studs and re-torquing head gaskets can be time consuming. ( Heavy Duty studs are torqued to 20-22 foot pounds vs the factory 13.7 – 15.2 pounds with stock studs.) And they resist stretching under running conditions. You MUST follow recommended factory tightening sequences.

 

Because of the above mentioned conditions, certain precautions and preparations are followed.

NOTE: Some automobile manufacturers do not even use gaskets because of close tolerances. ( They use fancy sealers or nothing.)

Here is what do:

When we install gaskets on HD's, Triumphs, Honda's, Kawasaki's the gasket surfaces must be true and not abused. Threebond #1104, Yamaha bond or Honda bond is applied to the gasket surface. This sealer is used for three reasons.

First: To help the gasket overcome any flaws or chrome on the surface.

Second: (Equally as important.) To manipulate and hold the gasket perfectly in place.

Third: Threebond will not fall off ( Like silicone) and cause blockage in critical areas.

Most engine builders use aerosol copper coat on head gaskets. ( 4-5 thin coats.)

It sounds funny (To some people) that copper coat is used on conventional gaskets rather than copper gaskets. ( It works great) And once again you MUST follow recommended factory tightening sequences.

The head gaskets are checked to make sure the dowel pins and head gasket holes are perfect before copper coat is applied. Dowel pins and head gaskets are checked because they are accurately positioned and manipulating the head gasket is not an option. Minor attention to head gasket dowel pin holes is common from time to time.

Example:

We had received a chrome valve cover (Yesterday) from a customer to install on his motor. Because we are aware of age, warping, chrome dripping and scrape marks, we checked the gasket surface.

This cover was so bad, even NASA space shuttle gaskets and sealer would not have helped.

Finally:

After the motor has been started and ran a few times, we will recheck torque spec's on all the covers. Most of the time they need to be re-torqued.

Most people re-torque head gaskets after a thousand miles or so. Especially if stock cylinder studs are used.

These procedures are what we do, and should be considered when installing any brand of gaskets.

 


Cafe tech 1.JPG (230024 bytes)  Adjustable cam chain  ( kinda)
Some racers spend a lot of time at high RPM's. 
Many aftermarket people sell manual cam chain adjustors.    ( for other brands )
Here is what the old timers did !!!!
You will notice the cam chain tensioner on the right has been tapped and a bolt has been installed to keep things in order or moving.
WE are not saying you will need to do this modification, but it makes sense.


 cafe tech 2.JPG (227120 bytes)   Modified  advance unit
 Some racers would weld the advance unit in  the full advance position for instant throttle response. 
Just some tid-bits from the old days. 
  

 

 

The 70’s (Exhaust and Tuning).


 For those of you that are to young or cannot remember, here is my opinion. Bike building in the 70's was very simplified; there were over a dozen catalogs to buy custom Honda parts, ranging from gas tanks, frames, wheels, front ends, exhaust systems, etc. We look at bikes from that 70’s era and can identify most every part as an aftermarket purchase. Now-a-days Hondas are much harder to build; every part must be hunted down or made from scratch. So the people who are building Hondas now-a days deserve a lot of credit.

Exhaust systems from the 70’s.
Many systems claimed horsepower increases, but many achieved minor gains by the fact less restrictive exhaust will show gains. Many systems used automobile collectors welded to there 4 into 1 system to save money. Primary exhaust tube diameter was a major issue with many systems, almost duplicating the factory diameter.

In my opinion, any 4 into 1 system is better than drag pipes and most other cool looking systems. Exhaust systems open up a world of theory, debate and experiences in tuning the internal combustion engine. The 4 into 1 system have been published as being tuned with velocity, shock waves or sound beats and the perfect amount of something engineered into them. When a cylinder fires and pushes exhaust down the pipe into a collector, the exiting gases are pulling exhaust gas from the other cylinders. So the 4 into 1 systems work well on muti-cylinder machines. Smaller primary pipes have been known for midrange punch. Shock waves or sound beats have been advertised as being the latest scientific breakthrough. We need to reflect back to our 2 stroke racing days to speak about sound beats. High performance 2 strokes live or die with shock waves. Some pipes are high RPM and some have torque characteristics. I remember cutting and shortening a brand new exhaust system to find higher RPMs for racing purposes. Finding the window of available horsepower getting smaller and smaller. So at what RPM did the exhaust system sold make horsepower?

We custom builders are in a unique situation. We want looks and we want horsepower with ground clearance. We do not have the luxury of shopping for a multitude of different pipes like the 70’s. Here’s my point… We built a bike we call the superbobber and the motor is highly modified (Compression, long duration cam, etc…) and the pipes are extremely long which we did for looks and shock value. We had never tuned or even seen a bike with pipes this long. With the combination of performance parts in this superbobber the normal train of thought would be to give this high performance bike a more generous amount of fuel. So the tuning process begins. Jetting, checking timing, adjusting valves, etc. The jetting process took longer than we anticipated because of a forgotten fundamental mindset needed to tune altered or modified motors. The mindset is if you go into a tuning process with a preconceived idea how a motor should be jetted, you will be wasting a lot of time. Example: Long duration cams help to pull in fuel, and the 4 into 1 exhaust is helping to pull exhaust out. Pressured intake systems help with an incoming charge of fuel. This would mean the bike needs a lot of fuel Right?
The superbobber is now tuned and the jetting is same as a stock motor. Most people find the final jetting on the superbobber unusual.

Back to exhaust systems. Due to the fact we have very few exhaust systems to select from. The only logical thing to do is select an exhaust you like and tune your bike as needed with a open mind. Honda 750s have a great potential to make power with the right combination of aftermarket parts. And have potential to run far better than the factory offered back then. There are a lot of theories about the internal combustion engine. But remember: Webster’s dictionary says: THEORY is a speculative plan, a conjecture, and a guess.

Thought maybe you would like to hear the superbobber story and maybe the preconceived jetting mindset might help you someday. Maybe you have an experience you would like to share?

___________________________________________________________________________________________________

Click to go Back to Honda Cafe Index

Cycle X

US Hwy 51 South

Hazelhurst, WI

54531

Phone: 1-715-356-7346

Email: cyclex@cyclexchange.net