Honda Shadow Running Lean – Pilot Jet
Here is a good example of a 1987 Honda Shadow VT700C that is running lean. Initially I thought it may be due to vacuum leaks, which are really common on older motorcycles. However, after checking for vacuum leaks & reading a few forums, I came to the conclusion that they come lean from the factory.
Service Manual
See this post for a FREE service manual.
Diagnosis and Solution
Some symptoms of a lean condition are:
- Having choke on for longer than usual
- Poor throttle response (hesitation, bog)
- Plug chop indicates lean plug color
I took apart the carburetors and cleaned them up using PineSol & Berryman Carb Dip to make sure it was not running lean due to plugged up jets (carbs were pretty clean and no plugged jets were found). Before cleaning the carbs, I checked the fuel mix screws to see how many turns out they were set at. To my surprise, they were out 4.5 turns! In my opinion, they are about to fall out! The Honda Shadow service manual states that the fuel screw should be turned out 3 turns initially. Below is picture that shows where the fuel adjustment screw is located. Keep in mind that there might be a welch plug installed from the factory to prevent adjustment.
In a previous post, How-To: Sizing Pilot Jet, I explain that the fuel screw setting needs to fall in the 1-3 turns out range. Since we are at 4.5 turns out on a fuel screw, a larger pilot jet will be needed.
The stock pilot jet for this model is a #38. I decided to increase it 2 sizes to #42, which gave me highest idle RPM at 3 turns out. It also greatly improved the throttle response as it was starving for fuel. If I were to do it again (taking these carbs out is not fun) I would have went to a #45 pilot jet and it may have have brought the fuel screw adjustment in at 2.5 turns or so.
Another jetting change I made is needle position. The needles are not adjustable, so I took some small washers totalling .040” thick and placed them under the needle to raise it up some. This provides more fuel in the ¼-1/2 throttle range. Coupled with a larger pilot jet, the throttle response has greatly improved. The power output has also increased.
Comments
Is your shadow running lean? Comment below.
I have the same bike Doing the same thing I Also put emgo slip ons on it and if I fallow your steps with the settings you put on here will I be ok thank you very much
Hi Josh,
You’ll be close. The slip ons will require additional jetting. Does Emgo have any recommendations in their instructions?
Im not sure I cant find any thing on them the mid and full are great its just the start off and its not poping on decel either thanks for your help
Then will I need to put a bigger main jet in too
Yes, you’re probably right.
This may be a silly question, but how long should the original pilot needle be? (Air/fuel mix). On a 1997 honda shadow ace 1100? I dont see any numbers on either one, and i suspect previous owner may have messed with them, being how the brass head(screwdriver part) is a little buggered up. Thanks for any advice.
I don’t have the dimensions available. If no numbers are marked, then buy a new jet. Who knows what you have.
Well my pilot is a 42 in my bike now what should I go up too
With the 42, how many turns out on fuel screw? Have you checked for vacuum & exhaust leaks? Your bike has 38 stock, right? I could have easily gone to 45, I would try that and see what happens. Order 48’s in case, they are pretty cheap.
It was 3 1/2 out no other leaks anywhere what should I do about the main its A 112 stock
Go up 1-2 sizes on pilot. You said it runs good at full throttle? Put in new plugs and do a plug chop at full throttle to see what color they are. You are probably going to have to cut the plug open to get a good look at the the entire porcelain portion of plug.
If you can call me I’ve got problems with the carbs on my wife’s 86 vt700 1(205)2154229 thanks andrew
Andrew, the best way to contact me is through email. Send me an email with all the info and I’ll try and help.
You still offering Shadow carb help???
Yes, what’s up.
Hi Matthew, First Let just say that I appreciate your advice! I have a 85 VT700c.
It runs great and then after about 30-40 minutes of riding, the right muffler gets very loud, and the bike doesn’t seem as responsive until I reach speeds around 55. I have replaced the plugs, CDI boxes and coils. I have also changed the fuel filter. I have not had the opportunity to clean the carbs yet.( just got this bike in Jan of this year) The air fuels screws are 3 turns out on left side and 2 turns out on right. I have played with these settings, which seems to help at first and then it goes back to the same issue. So I believe that I should clean the carbs, what should I buy to prepare for this? Thanks for your help.
Tony,
I have to say that 80-90% of problems I come across are carb related. Also, your fuel screws need to be adjusted the same amount of turns out. Take a look at your plugs when the bike is acting up, I bet it is lean. Download the service manual, it should give you an idea of tools that you need.
Hi Matthew, Just want to say thanks again. I finally got around taking off the carbs and cleaning them…found a lot of debris! This was my first time cleaning the carbs and it was actually a lot easier than I expected. (I was intimidated by this task for some reason!) You put out some of the best how to presentations that I have seen.
Thanks again, your advice is excellent!
Thanks, Tony!
Hope the carb clean did the trick.
Great Job!! Your videos are so clear and easy to follow 🙂 Appreciate what you do. I have a couple questions:
1. Would you say that bikes start to need a little more fuel as the miles add up? Say the factory settings were just rich enough to avoid lean symptoms but now with a few extra miles a half turn out on the mixture screw does wonders?
2. What if on a stock 4 cylinder bike turning mixture screws doesn’t have much of an effect? Should you effectively be able to shut down that one cylinder via the mixture screw like on a twin or are fours just less sensitive since each cylinder is only carrying a quarter of the load?
3. And lastly, on a plug read, having installed a clean plug how long should a properly warmed engine run under a specific throttle opening for the plug to give a decent reading? Will a few seconds be enough?
Look forward to seeing your site grow along with your popularity.
Have a great one.
Thanks, Tansen!
1. I would say that carbs tend to get dirty over the years and will cause bike to run leaner. A thin layer of varnish is all it takes on the pilot circuit.
2. The screws should be responsive. Make sure idle is low. You should be able to close the screw and kill the motor. I’ve had non responsive screws that I was able to turn in all the way and it was still running, meaning the pilots were too rich (fuel screw). On multiple cylinder engines, you should have all screws out the same number of turns and then determine if RPM has changed.
3. First, change plugs on warm engine. If tuning the main for example, a WOT through a couple of gears should give you a reading. I would say 15-30 seconds.
Thanks a bunch for sharing your knowledge. Tinkering with bikes can be a downright disease and it’s so great to be able to share info.
Aloha from Maui!
No problem! I wish I were in Maui right now, it’s around 20°F here right now.
How do I cure a constant popping on the deceleration
That is a lean condition. Is the bike stock? Exhaust or air filter non OEM?
Start by checking for vacuum leaks and then tuning fuel screws/pilot jet:
https://howtomotorcyclerepair.com/how-to-size-your-pilot-jet-pilot-screw-explained/
Matt
My 89 vt600 has no power when i hit 4th gear and lightly hit the throttle. 1/4 turn on the throttle between gears and it is starving for something . I did some jetting and threw on some pod filters i have straight pipes. I went with 45 pilots and 128 mains . Plus one shim on eAch slide needle… It takes off with more power than before but if I’m going uphill and go through the gears it is hesitant between gears. what should i do to fix this? If you need more information let me know… Anything will be greatly appreciated!!!!
MG,
How many turns out are you on the fuel screw?
Here is a simple test you can perform to sure if you are running lean. Take some masking tape and tape up the pods, blocking 25-50% of airflow. If symptoms improve or disappear, you are lean and need more fuel. 1/4 throttle would be the transition from pilot jet to needle with some overlap.
I’m 3 turns out on each af screw. I added one more washer on each slide needle. I did turn the af screws all the way in lightly seating them and the bike didn’t shut off…i still have the oem 40 pilot jets . . . The housing for the oil pressure switch is cracked. So I can’t run the bike today. The bike runs with the wire for the switch disconnected . Should i jb weld the crack or should i delete the switch and hose clamp a rubber plug over the housing?
The oem jets are not on but i have em handy if I need them
I would repair the oil pressure switch.
If the engine will not die with screws turned all the way in, then there is a problem. Turning the screws should also make a difference. I’ve run into this several times and each time it has been a different cause, so I will list some things to look for:
1. Make sure choke plungers are in good shape. They need to seal the port that delivers fuel for cold starts. Make sure cable is properly adjusted. 2. Check for vacuum leaks.
3. Make sure float level is in spec and float needles in good shape. 4. The needle does supply a “little” bit of fuel at idle.
5. Synch the carbs.
How do the plugs look? Pull them and upload a pic.
Matt
K I’ll check all that and do a plug chop … Gonna order some shorty choke knobs from tjbrutal customs. I’m pulling the motor now to do a good repair on the oil leak. Just pulled the exhaust ordered new exhaust gaskets . So its gonna be a week or less until i can start the bike… Gonna go thru the carbs again and double check everything. I did set the float level to factory specs . One thing i did notice is there isn’t a washer on the float needle seat soo that could be part of the problem too. Thanks for all of your information i will definitely put it to good use!!! Stay tuned . I’ll update you once i get everything installed . P.s. The plugs were black .
The one on the right is an old pug from the old carb setup
The one on the left is the one I replaced in the same cylinder with the new jet setup and pods
OK, this is starting to make sense. Your float level will be higher w/o a washer. Your engine will not die when screws are turned in since it is running rich and pulling fuel from somewhere else….like too high of a float level.
I just checked the chokes and they were fine i did a little house keeping while i was in there. So I guess I’ll get some washers and recheck the float level… By chance do you know the thickness of the washer in question? I did some looking and can’t seem to find it. Thanks in advance!! You have been a huge help !!!!
They are probably a good 1.5-2mm thk. Unfortunately, I think they only come with new seats and needles which can run 30-40ea. Maybe keyster or other aftermarket can save you a bit. You are basically looking for a metric aluminum sealing washer.
Finally I checked the intake valves tgey were way off I put them to factory spec and its running 90 times better. The only issue I’m having is at higher rpms it spudders maybe more fuel? There was water in the tank i got all of it out . I rode it about 20 miles today . Takes off great . Time for some fine tuning maybe. I also synchronized the carbs
Sounds like you are making great progress. Tell me more about the sputter. At what RPM/throttle position?
About 3/4 throttle to full throttle it hesitates spudders… I just got some 130 main jets in today . I’m gonna try and get to it before the weekend. If that doesn’t fix it …. I’ll have to drop it at a shop 🙁
I noticed the rear cylinder isn’t running too hot it’s pretty cool comparing to the front . Also you can se when i put my hand on the exhaust it has some suction. I’m thinking the intake valve is open during the exhaust cycle. Time to check the valves again. This my first bike and I’m trying to do all of the work myself I guess I’m still learning 😉
http://youtu.be/c4U454NMFIY
Pull all the plugs and read them. The rear cylinder plugs are either fouled or not getting fuel.
I have a vtx 600 1997. I have duel carbs and I rebuilt them with stock jetting. I tuned out idle fuel mixture screw out about 3 times then road great. Then drove another day then started to run lean so I turned out to 4.5 turns ran great. then the next day started to run lean again. I have stock air box on it. Not sure whats wrong.
Check for vacuum leaks: https://howtomotorcyclerepair.com/how-to-diagnose-motorcycle-vaccum-leaks/
I did. I sprayed to see if there was any. But I found that I turned the idle screw so far out it came out of thread and was missing but I put back the old one I had. I turned them both out about 3 tunes and it runs but it runs lean. Hesitates and pops a little on deceleration. Can I tape up some of the air flow or should I get bigger jets? If so what size should I get?
Idle screw? You mean pilot fuel screw?
Are there any modifications like air cleaner or exhaust?
Thank for the informative article! I recently got a 1986 VT700c. It’s running lean- idles unevenly, hesitates and jumps on acceleration, and jerks on deceleration. I changed the spark plugs (which were white-ish) and the fuel filter in the hope it would help, but no luck yet. I’m going to try the pilot screw next, hopefully it does the trick!
No problem. Could also be that the carbs are getting a bit dirty as well.
Hi Matthew, I have a 2004 Honda Shadow Spirit VT1100c with Vans & Hines pipes on it when I purchased it. The bike is very loud and back fires on deceleration. My guess is bike is getting to much air and I may need bigger main jet. I still have the stock exhaust(got it also when I purchased the bike) and am thinking on going back. Do you think going back will solve the issue or going to a bigger main jet?
Backfiring/popping decel is all in the pilot jet/fuel screw tuning. You likely need larger pilot jets and/or richer fuel screw settings.
More on this topic here: https://howtomotorcyclerepair.com/how-to-size-your-pilot-jet-pilot-screw-explained/