Special Tuning Tips for ’77 GL1000s + Carb Top Service

You might consider this item: Randakk’s GL1000 Carb Rebuild Video

Honda made a number of jetting tweaks in ’76 (K1 and LTD) and again in ’77 (K2) for US-bound GL1000s to cope with tightening emissions regulations. Other markets were affected as well. Honda necessarily made the bikes progressively leaner through these model years. Social responsibility is a good thing for large corporations, but these were not great moves from the rider’s point of view. Riding a bike with overly lean carburetion may be “green,” but it certainly can be frustrating.

In my experience, the best running stock GL1000 is the ’75 (K0) model closely followed by the ’76. I find that the ’77 model is by far the worst of the lot.

In addition to the universal off-idle glitch (easy to fix – see below) that all early GL1000s exhibit, the ’77 also suffers from a dreadful midrange hesitation as well. Once, you get the revs above 4000 rpms (relying on the main jets), the performance for the ’77 spec. jetting is fine. However, from 2,500-3,500 rpms in light load cruising situations (1/4 – 1/2 throttle), the poor throttle response is very annoying. Here’s what I do.

Preliminaries:

• First make sure all your tune-up issues are in order…esp. valve clearances and ignition. Breaker points and timing must be perfect.

• Take steps necessary to insure that you are working on carbs which are meticulously clean (on the inside). If you carbs need overhaul and cleaning, bite the bullet and take care of this before you proceed. The “fix” detailed below won’t cure problems caused by crud inside your carbs!

• Make sure you’ve already implemented the “off-idle fix” detailed in another tech tip below. This is an easy (external) change of the pilot air jets. A MUST for all early GL1000s!

• This special fix for ’77s is easier to implement as part of a general carb overhaul with the carbs off the bike. However, here I describe how to do the “fix” on a bike that has no other problems.

Here’s the cure. What you’re trying to accomplish is gaining enough access to allow removal of the carb tops. First, remove the air filter lid, filter and housing. Next, detach the air-cutoff valve (don’t lose the o-rings!). You will also need to detach the fuel line at the fuel pump and remove the 8 acorn head nuts/bolts that attach the intakes to the cylinder head. Important: block the intake ports with rags or tape to prevent anything from falling inside.

Now you can maneuver the entire carb assembly from side to side to gain access to the screws that secure the carb tops. I usually loosen the intakes on the right side and rotate them 180 degrees to gain additional working space. If you prefer, you can go ahead and remove the choke cable and throttle cables and remove the entire carb assembly from the bike. I prefer not to mess with the throttle cables unless there’s a good reason to do so.

Do one carb at a time as follows. Exercise care handling these parts as they are easily lost and/or damaged. Please note that step 4 is only thing mentioned that is unique to the ’77 GL1000 …the rest is a good description of upper carb maintenance for any early GL1000:

1. Remove one carb top, slide with needle and spring. For later reference, take note of how much “wiggle” you have in a fully secured needle.

2. Remove grub screw from inside slide (this screw secures jet needle in position in the slide).

3. Remove jet needle from slide

4. Slip one #4 stainless steel miniature washer onto the jet needle and reinstall the jet needle into the slide. Note: I’m NOT referring to a 4 mm washer. A #4 miniature washer is a very small “inch” size. These can be purchased at any decent Ace Hardware store. These are not made to tight tolerances. Make sure you pick 4 reasonably matched washers free of burrs or other machining defects…especially on the “flats.” You may have to dress the washers a bit with crocus cloth. The diameter of the hole in the washers should be a near perfect fit to the upper straight segment of the needle. Likewise, the outer diameter of the washer should approximate the dimension of the “head” of the needle. The ideal washer will have an outside diameter of no more than about 0.25″…if it’s much larger it will foul on the internal surfaces of the slide and give you much more correction than you are seeking. The approximate thickness of your washers should be about 0.018 inches. If you use a thicker washer, you will risk an over-rich result replete with plug fouling.

5. If you strike out at your local hardware store, go to the nearest Nut and Bolt distributor and ask them to order a quantity of the following washers: MS15795-803. This is the military spec for a stainless steel washer of the size you need. This is a fairly low quality spec (by military standards), but plenty good for this application. You may have to order a minimum quantity of 250 or so. Fortunately, they are not very expensive. Also, many aviation maintenance shops should have these MS15795-803 washers on hand and should be willing to sell you just a few of them, instead of ordering 250…thanks to Steven Brinly for this tip!

6. Important: put several drops of medium duty Lock-Tite (blue not red!) on the grub screw then reinstall and tighten the screw fully, then back out the screw 1/8 turn. The introduction of the washer corrupts the designed-in geometry of the components. Backing out the grub screw slightly will allow you to re-capture the needle “float” you observed in step #1. Set aside the re-assembled slide/needle assembly for now.

7. Remove the kidney shaped plate and gasket that covers the air jets on the top of the main carb body.

8. Check to make sure the air jets are not REVERSED. The correct orientation is for the jet with the larger orifice (#120) to be outboard. The jet with the smaller orifice (#60) should be inboard. Correct the placement of these jets if necessary and say a curse to Mr. Clymer! Replace the gasket and kidney-shaped cover.

9. Using crocus cloth and light oil (like WD-40) gently polish the inner surface of the carb top and the external “piston” contact areas of the slide. Also, clean the inner bore brass bushing of the carb top using a suitable wooden dowel wrapped with a bit of crocus cloth. Don’t be aggressive! You’re not trying to remove any metal, just clean and smooth the mating surfaces. Note: a better way to clean the carb top inner bores is to use a 40/41/10 mm caliber bronze phosphor handgun bore brush (available at any gun Shop)

10. Check the carb top to make sure that the small relief port near the junction point where the cap cylinder joins the top of the cap is open and clear. I use compressed air to do this.

11. Clean the top and slide using contact cleaner. DO THIS OUTDOORS!

12. Dry the top and slide carefully with compressed air.

13. Do final cleaning of top and slide using a soft clean rag.

14. Test fit slide into carb top. The slide should glide in and out with no discernible friction. If there’s ANY sticking, repeat steps 9-14 as necessary until the result is satisfactory.

15. I like to test for proper vacuum response with a simple test. Position the slide in the carb top (w/o spring). Pull the slide out until the piston portion just engages the top. Hold the whole assembly with the slide horizontal. Now using my mouth, I apply a slight suction to the bottom of the slide…there are several transfer ports adjacent the spot were the jet needle emerges. Obviously, the sharp end of the jet needle goes inside your mouth so be careful! When you apply a gently suction as described, the slide should zing crisply up into the cap. If not, investigate and correct before proceeding (a broken or defective cap “button” is the likely culprit).

16. Place slide w/jet needle into the carb body taking care to engage the locating pin for correct orientation. Make sure jet needle lines up with corresponding needle jet. DO NOT FORCE! Check for smooth up/down movement with no binding.

17. Install spring.

18. Install cap taking care to make sure spring is centered on carb top post. Secure carb top mounting screws. DO NOT USE ANY LUBRICANT ON THE SLIDE OR CAP!

19. Now repeat steps 1-18 for the other 3 carbs.

Inspect the intake o-rings and replace if the condition is in doubt. Carefully, re-connect the intakes, fuel hose and air cutoff valve. Replace the air filter assembly. Reattach the crankcase vent hose. Go for test ride. You should be very pleased with the results. The key is smooth operation of the carb slides plus the critical addition of the shim washer (step # 4). Unlike a dirt bike carb, the GL1000 needles are “nonadjustable” This is true for most carbs that have two sets of main jets: primary and secondary. However, adding the washer effectively raises the needle slightly and thereby enriches the midrange just enough to reduce or eliminate the midrange hesitation overcoming the factory imposed lean condition. Don’t be tempted to add two washers instead of one. You will not improve your results and you will introduce new problems you’d rather not deal with.

Total investment will be about 40 cents for washers + your time.

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